Archery: I think the only skill tree that kind of needs revamping is archery, and it seriously needs a change. I personally don't play stamina but from what I hear from other players, it just seems like all its good for is a damage over time, and sitting on top of keeps trying to 1-hit players with snipe. From what it looks like to me, the usefulness of archery is this:

DoT: Poison Arrow (+morphs)
Spammable: Nothing that produces good dps
AoE: Nothing decent really
AoE DoT: Volley (+morphs)
Utility: There's a few stuns, but only half decent one is Focused aim (reduces target armour).

So I propose that the archery skill gets a re-vamp to account for each of these types of skill, because most of the other skill trees have something for each of these types. I think the utility skill could be really interesting as you could try to incorporate things such as reduce damage, increase targets cost of abilities or similar by making a skill called something like "Target Weaknesses" or something.
That's just my take on archery, but there are a lot of people out there who yearn for a more intricate and productive archery overhaul, because let's be honest, archery in this game pales in comparison to archery in other games, such as Skyrim (yes I know Skyrim is single-player so cant be the same).

Stamina: Okay so I have to give it to ZOS, it looks like they did a good job at rebalancing stamina in the upcoming update, but I still think there are a few things that were overlooked.
The first thing is healing, and this is subjective to opinion. But I'll mention it anyway. There are basically no stamina heals I can think of, other than Vigor and Rally, and this can't even be compared to skills such as BoL, Healing Springs or Healing Ward. I think stamina at least need a self-heal for every class, so then this gives them the opportunity to complete harder content such as vMA, by giving them heals that benefit from their preferred playstyle (stamina). Some however, think that the additional shields and damage negating abilities you get with stamina balance these out.
The second thing is stam sorcs. I personally don't play a stam sorc, but from what I can hear from others, your much better off going a magicka sorc or even rerolling a completely different class if your set on stamina. With the upcoming patch, it seems like magicka/stamina is more or less balanced between each individual class, except for sorcerers. Magicka sorcs produce WAY more dps than stamina sorcs, and I think stam sorcs just need a bit more loving.

All Classes: Again, first impressions seem like ZOS did quite a good job in the upcoming patch at balancing all classes, but I still think there's more to be done. This is specifically in retrospect to healing. Templars are by far the best healers in the game, and most other classes barely have one spammable heal ally spell, let alone an entire tree dedicated to the role. The remaining three classes need more healing abilities, so the we can see a bit more variation and encourage freedom of playstyle a little better, since you don't have to be one particular class in order to heal.
Templars: Now, I play a templar so this may just be a biased opinion, but I believe that templars need some mobility. We don't seem to have any skills that increase our movement speed or anything that will just generally make us faster, except for an aedric spear charge. I don't know about other classes but this seems to be a problem among templars. Maybe we could make the other morph of restoring aura increase our movement speed for a bit instead of giving a bit more regeneration?

One of the things that frustrates me in this game is the gear, but not as you might expect. I get frustrated with the fact that there is only ever a few best in slot gear sets, and the rest are worthless. For example, if you want to do magicka dps, you need to be wearing julianos, twice born star or some argue scathing mage and spell power cure. It doesn't matter what class or playstyle your going for, those gear sets are what you need to produce the best numbers. If you go into a dungeon wearing a set designed for magicka dps but isnt one of those sets, someone in your group will probably tell you that you need to change it to one of the sets mentioned above. It seems that there are only ever a few desirable gear sets in the game, and all the others are rendered useless because their 5 piece is just not comparable, due to the differences in their potential. ZOS keep bringing in gear sets and yet most likely none of them will actually ever be used, because of how good these few 'BiS' gear sets are. Now for some people there's nothing wrong with this, but what I want is a bit more variation in the game. I think ZOS should take a long hard look at all of the gear sets, and rebalance all the unused gear so that people can now choose gear depending more on your playstyle and abilities. For example, you might want to choose a set that increases your cold damage, if your using a lot of those abilities. Or you might choose a set that spawns other things to attack the enemy alongside you, and another that maybe increases their damage, if you like the idea of having lots of enemies attack the target. They need to encourage the 5-piece sets because that's what makes each set unique. Now this is mainly focused for PvE and not PvP, but even in PvP there are a few sets that are designed for PvP that people just don't really seem to use, like powerful assault or reactive armour. I really think changing all the gear would make the game have more variety, and lots more options for allowing you to play as you want to play, and still be able to do the harder content.

Repeatable content: I think ZOS need to have a look at the kind of repeatable content they currently have in the game and are bringing into the game. Its great that they're trying to get players to have things to do each day, but quite frankly most of the repeatable content is boring. It is always the same, and most of the time you want to get it out of the way quickly so you rush it, making it seem even more boring. It just needs to perhaps vary a bit more, just so that people are not doing the same thing over and over again, because that very quickly gets dull. I don't quite know how ZOS could do this, but I'm sure they could think of a way to just perhaps make it a bit more interesting for everyone.
Mini-Games: Now this is kind of stemming from the idea that we need to have fun, repeatable content for players to enjoy. I've got two types of mini-games that I think would work brilliantly in ESO and would bring in so much more fun and excitement into the game.
The first is a "Capture the Flag" type minigame, which I'm sure all of you know the basic premises of. It would have to be PvP and be who can capture the most flags in a time limit, and I think ZOS could make this really exciting. There could be 2 teams, that you could either choose or be randomly placed into, the Aedra vs the Daedra. There wouldn't be much difference except their base and potentially the things/outfits that mark the players out to be on that side. You could even make things really interesting by coming up with the idea of 3 teams, and have 1 team for each alliance. 3 team capture the flag would be so intense and so much fun. You could even allow people to choose what alliance they went into, by placing the mini-game in a daedric realm, and come up with the idea that the "Alliance leaders" are actually just daedra in disguise, similar to how you did that one stage fight in the mage's guild storyline. That way it wouldn't matter which alliance you picked, and this would help balance teams out easier.
The second is an "Arena". Now this is a hot topic that I don't see why ZOS haven't brought in yet, but let me add my ideas to the pot. For those who don't know, it would be an area where you can choose to battle others players. You would be whisked away into a separate instance, with you and your opponent, and whoever dies loses. This could be made really interesting, by making some sort of set-up and rules menu pop up before your arena. You and your opponent could choose to toggle on/off things like obstacles, gear, battle levelling, ultimates, other aggressive NPC's, etc. You could also choose to do stakes (bets) between battles. I think a really interesting idea would be to expand on the basic 1v1 idea and perhaps have up to 12v12, or even guild vs guild. You could also perhaps do a deathmatch mode, where its 1v1v1, or maybe up to say 10 players all against each other.
Now all of these Mini-games would be tricky to place into the game, but I really think they would help introduce much more exciting content, especially to players who don't like the current PvP. I think ZOS could introduce these in a number of different ways. They could add them into a new "no-man's land" zone, meaning all three alliances can go there, or perhaps even just place them in craglorn. You would have to change craglorn so that all three alliances can go there and see each other at the same time (if its not already), or perhaps just make those mini-game lobbies have this feature, and that way (if they were placed in craglorn) it would revive parts of this old mostly dead content by placing some more fun stuff in the area. ZOS could also sell it off as a "free-DLC", which would serve as a great marketing tool to get more players into the game, similar to how they introduced everyone to craglorn for free.
Rewards: Now I think these rewards can be given to both repeatable content and mini-games, so that they may perhaps have a bit more incentive to partake in them, other than just fun. They could perhaps get tokens after each game to spend in a shop selling all the rewards. My ideas for good rewards are as follows:
Levelled consumables (similarly levelled to as in the crown store: food, potions, soul gems, etc), gear sets (could be either revived old sets or new ones that benefit these mini-games), experience rewards (could have them for character experience or maybe individual skill line experience), leaderboards and cosmetics (mounts pets, costumes and titles). You could have more that's just what I came up with from the top of my head.

Now this is kind of where my ideas go a bit more controversial. I believe that many new players are either not buying the game, or quitting very early on, due to one simple factor. There is no proper content at lower levels. From the start of ESO you are forced to grind because you just try to race to level 50, because thats where all the content is! ZOS focuses too much on what the current, high levelled players want and they don't focus on getting new players into the game or getting them to stay! The only content at lower levels is questing in zones, pvp and normal dungeons. Pvp is good because it is fun and different all the time, but not many players can do it at low levels because the experience given from it is garbage. You can spend a month in Pvp and level the same amoutn as you would inn 2 days of PvE grinding. Therefore strictly PvP'ers never level up and reach all this end-game content, so to get there they are being forced to quest grind. I can't emphasize how much ZOS need to focus more on getting players to buy the game in the first place or stay once they have brought it, because not many people are due to the lower levels just not being that fun.
So, my idea of countering this is to massively reduce the effect of gear (set bonus', armour/damage), each level and champion points in order to make it so there isn't so much of a difference in 'ability' of players. Even a level 50 with 100 champ points pales in comparison to a level 50 with 200 champ points, even if they have the same gear and stuff. There is too much of a difference between players, so therefore most new players are unable to join in with most of the content because they have to get to end-game in order to be good and also sometimes just get completely obliterated/hated on by the pro players. Now I've heard from some players that in WoW you cannot have a really terrible player and a really amazing player. I've never played the game so can't say for certain, but even if its not true and we strived for this regardless then it would reduce the need for grinding and also introduce the new, lower levelled players into currently end-game locked content, such as normal/vet dungeons, dsa, trials etc. Now that sounds crazy to some but only because there is currently such a HUGE difference between players, in terms of what they can hit and how much sustain they have. Someone could go from being able to cast 5 Dark Flare's that hit 10k each before they run out of magicka, to someone being able to cast 30 that hit 40k each. I think if the differences were thinned out, it wouldn't sound like such a crazy idea. This would give new players something to do besides grind to the higher levels, because they'd actually be able to enjoy most of the game without the need for just a pointless grind. And yes, I don't mean just get rid of levelling or make all levels the same, but basically I'm suggesting it should be madeso that it gives you an advantage, but not such a huge one. Now I'm not talking about getting level 10's into level 50 content, but I'm more about making it so a good level 30, could play the content and excel in it just as much as a new level 50. I think the middle levels should be able to join in and not be pushed away by the fact that they just don't have enough spell damage or max magicka. There should obviously still be a difference between each level and champion point to encourage people to level and provide incentive, but this can be compensated for actual real-life skill, other than how much time you've spent killing mobs over and over. For example, a great level 30 player would never be able to beat a kinda bad level 50 with 100 champion points in dps now, but if these changes were applied then they could easily overtake them when it comes to dps. These changes would give newer players a chance to experience this new, high-end content better. It could perhaps, similarly to PvP, be locked until they reach a certain level, perhaps level 20. Now I get that some may hate this idea, but perhaps ZOS could even get rid of the level requirement for gear and just have all at end-game status. That way if a lower level entered some end-game content, they could be battle levelled not be held back by their gear. And as I mentioned earlier, the gear they have shouldn't matter if its not "best in slot", because all should be rebalanced so that more or less all gear is "best in slot", provided your using a 5-piece that benefits your playstyle. If ZOS didn't want to remove the gear level requirement, which I understand, then I think they should change the battle levelling so that it actually reflects your current attribute distribution and gear. It would give you the stats that you would have at level 50, if you continued using the same attribute point ratio that you do now, and if your current gear was level 160CP, instead of level 20. I think this would be great for new players to be able to get stuck into the game early, and enjoy the content, not forcing them to grind 24/7.
However, if we really want to reduce the grind then we should make everything in the game give roughly the same xp/hour, whether that's questing, doing dungeons, endlessly killing mobs, PvP, DSA, trials, whatever! ZOS could add experience rewards at the end of each dungeon or trial or mini-game (see above), like they do with the random dungeon mode in group finder, so that players can do these to level instead of mob grinding. I think this is an idea we can all get behind, because at the moment the best xp/hour is grinding mobs, no question about it. However, if it were all revamped so that everything gave roughly the same experience per hour, lower levelled players could branch out and do as they liked, and still get great xp for it and level up at a pace they feel happy at. This would make it so that people are locked into one type of content until they hit 501 champion points.

Lets be honest, the game is far too easy now. All dps is just going up and up and up and difficulty is remaining the same, meaning that content difficult at the beginning is just ridiculously easy now. Even average players can pull 15k-20k+ dps single target, which used to be exceptional back in the day. Most pro players can hit 30-35k and some even like 45k-50k! I've heard of people who can solo 4-man veteran dungeons no problem, do trials with like 4 people or DSA with like 2 people. People are getting too good at the game and with all the class rebalancing and new gear sets added into the game, dps is just increasing so quick, but everything else is being kept the same. I think once ZOS balance out all levels and compensate for difference in ability as I mentioned above, ZOS would need to check the difficulty of everything and see if it needs to be made harder or not. They would have to be careful though, because some players hate a really difficult game. This makes difficulty in games a very subjective idea.
However, I believe I have a solution. ZOS should add a new tier of difficulty, a legendary mode, to dungeons, trials, or content such as DSA, which is exactly the same as veteran but just monsters hit say, 2x more and have 2x more health! This would mean that players who prefer the harder content could utilise this new difficulty, whereas players who don't can stick with the old ones. Now exceptional new gear was added to these new modes then ZOS wouldn't be achieving anything, because things would just go backwards to how they do now. Instead, I think they should create a bucket load more achievements to this new, harder mode, and use these to add new titles, dyes, or even costumes, mounts and pets! To give people a bit more of a solid incentive though, ZOS could change the drop-rates in this dungeon for those higher-end gear sets, so that they drop a bit more frequently. For example, if you were running DSA at legendary difficulty, then you would have an increased chance of a master weapon at the end chest. This would compensate for all types of players, as people would not feel forced into this harder content unless they wanted the new cosmetics, but would still be able to obtain those higher-end items, just that it would take a bit more time to obtain.
Now, one other side-note, is that I would really like to see dragonstar arena make an entrance back into the game. I've mentioned it a few times in my post because it makes for a good example, but people just don't run it anymore because the loot is just not worthwhile. If the loot was scaled up to CP160 then it would bring much more people into this content.