
ESO is an MMO.
ESO is an RPG.
ESO is an Elder Scrolls game.
ESO is not a single-player Skyrim sequel.
The most painful thing is, that the user interface in ESO has been the biggest issue by a large margin that has ever impacted my having fun in the game. Unfortunately, this also has had very wide-reaching effects on every major issue that has been a firestorm on the forums recently, too.
Combat UI features have largely left the vast majority of players having no idea how the mechanics really work (addons being the only way to see any numbers, which until the Imperial City launches will (since mid-beta) have been unable to tell you who hit you, or what skill you were attacked with, let alone what buffs you have on your character or debuffs you've cast on others, or who/what healed you... other things like a basic combat log tab to enable on the chat box have hurt this as well, with the same restrictions on addons until the upcoming DLC, and no way to do so ever before).
Industry standard features became that for a reason, and it's not because most people hated them and they were useless

. I feel the game's major issues stack up like this:
The #1 issue long-term players have (and in the past have had, regarding people who have quit) with the game, that really needs to be addressed.
I'd say
mechanics and combat info clock in right at #2which lead to people getting fed up with Veteran Ranks originally as the game difficulty increased when going into that level range and they didn't have any way to tell how to handle it because of that, which is also part of the UI.#3 would probably be the slower pace of content updates, particularly on the PVP end of things, but you can't change the past 
and the Imperial City is almost here

!
More looks to be coming at a better pace in near future overall.A moderate distance away as #4 would be the champion system, which is having little honest discussion as virtually everyone who posts about it doesn't know how any of it works or how it affects things in-game because of points #1 and #2... and misguidedly demand severe nerfs rather than relatively easy tweaks such as a moderate scale-down , implementing the catch-up mechanism sooner, or adding another 36 passives but leaving the cap at 3600 champion points to make it into a true customization aspect as well.
Direct UI features ranging from needing addons to have basic game functions, to addons not being allowed to even try to take up the slack for many options such as nameplate/guildtag toggles, to outright bugs (group leader bug... stuck health bars... cursor mode randomly triggering after closing UI windows and requiring a /reloadui... party members entering combat as you load a new zone causing it to hang up and give you an endless load screen) along with the lack of general usability, have also been a bear

.
Community features like optional toggles for name/guild tags and player titles, being able to recognize/see friends and guildmates in the area readily, the deathspam channel in Cyrodiil which gave it a feeling of activity and life, simple things like showing what sold in a guild kiosk mail or having a "Reply" button to message someone back in the mailbox.
Consoles not only have all of the issues above... but can't use addons due to Sony/Microsoft platform restrictions in the first place, and don't have even a chat window you can pull up when in say your inventory or on its own screen, instead relying solely on voice chat which has a myriad number of its own inherent issues when being used as the only real form of communication. Both text chat and voice chat have their uses including some overlapping ones, but neither can really handle everything the best.
(Obligatory "ZOS plz fix!" goes here)
Edited by Attorneyatlawl on July 23, 2015 11:45PM -First-Wave Closed Beta Tester of the Psijic Order, aka the 0.016 percent.
Exploits suck. Don't blame just the game, blame the players abusing them!
-Playing since July 2013, back when we had a killspam channel in Cyrodiil and the lands of Tamriel were roamed by dinosaurs.
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-In-game mains abound with "Nerf" in their name. As I am asked occasionally, I do not play on anything but the PC NA Megaserver at this time.