I've been having a blast leveling mine. As far as end game PvE I don't think you'll have anyone begging for you to bring your magden but they seem like they could be pretty strong in small group PvP/battlegrounds. Very fun regardless.

It's not in great shape for PVE damage-dealing. A good player can pull off a very good target dummy parse with magwarden, but that requires using the Bear ult, which is an no-go in some trials. The reason for this is that, while the bear does very good damage, it also behaves like a low-skilled player on their first day in the game, standing in high-damage AOEs, charging off to the wrong place for no reason, and easily getting killed. Plus you can't reasonably do much to keep it alive. A magwarden without the bear is just a less-good version of other classes, unfortunately. Add to all this that magwarden DDs bring no unique synergies or group buffs, and you have a recipe for a class that's not worth playing at endgame.

As a PVE tank or healer, warden is in great shape. IMO 1 magwarden + 1 magplar is the optimal healer setup.

I enjoy playing my magden in dungeons/arenas end game. It won’t look as great on a dummy parse as other mag classes can, but in practice it’s good, e.g., I’m usually pulling around a third of group dps in ST fights with two other nightblade dps and usually pulling upwards of half the group dps in AoE fights (with two nightblades, closer to 45% when with a sorc). I’m assuming it’s pretty good in trials too (at least for those where pets are allowed), but frame rate drops and latency prevent me from really having a good picture of how good it could be there.

People will complain and I wouldn’t necessarily mind some buffs (for example some sort of group buff/synergy), but it’s hyperbolic to call the build dead.

As question is about magden in PvE I will not go into other specs details.

In general magicka spec of this class is versatile. Even if you choose to be a DD you can easily respec to healer later because of Green Balance skill tree. Whether you are group player or you prefer to conquer obstacles solo - warden fares well in both scenarios due to good damage output in group content and ability to stay alive due to potent defensive buffs and heals from Winter's Embrace and Green Balance skill trees if you choose to fight alone.

I've been maining magden as DD (and Warden class in general) for several months right now and well... It's not as bad as people think it is. With proper gear, elemental weapon as spammable and bear ultimate it can deal decent damage. Due to extremely low cost of bear ultimate it is in fact only class that can provide ranged Major Slayer with Master Architect set, which is (imho) essential if you want to deal damage comparable to other classes (not counting nightblades obviously, they still are kings of DPS due to their kit).

Contrary to what some people say you can use bear in any content you want including trials IF you learn how to control it (like keeping it stationary during vAA Mage fight so it won't spread Chain Lightning, or turning bear into Passive mode [Y+Rightclick] during certain phases of Assembly General fight in vHoF). Yes, it sometimes dies, but to be honest it doesn't happen too often. Not with amount of heals happening in trials.

For gear, as mentioned above, I strongly recommend using Master Architect and building around it. I personally use Master Architect + Mother's Sorrow setup which yields best results for me. Reaching 50k+ dps in trials is not a big issue with it. Practice your rotation, watch your DoT's and buffs and I guarantee you that you won't be disappointed. It's really fun to play class after all

My bars for reference (double inferno staff, Master Architect Infused front, Maelstrom Infused backbar):
<Bar 1> Elemental drain/Crushing Shock (you want it for Ancient Knowledge passive) | Fetcher Infection | Elemental Weapon | Blue Betty | Inner Light | [Bear Ult] (You want to activate ultimate on this bar as only here you have Master Architect's 5-piece)
<Bar 2> Winter's Revenge | Elemental Blockade | Harness Magicka | Channeled Acceleration | Inner Light | [Bear Ult].]

That being said I cannot lie that warden class is in perfect state of course. It lacks a hard CC. Any hard cc, stun/fear would be godsend. In PvP magdens are kind of forced into using Master's staves if they want any reliable CC in their kit (clench in general, but it's high cost forces usage of Master's staves). Bear's behaviour can be problematic. If you are good with controlling it manually it is ok, but our furry pal could use a bit better AI, cause he can sometimes... Get overwhelmed by reality if nobody is watching over him. While speaking about bear - class has no real execute. Of course, bear hits like a truck in execute phase but remember that it is an ultimate. Even with low cost it cannot be used as a reliable form of executing. There are much more pain points, most stated here. That being said - class has it's flaws but is really fun to play and with few adjustments to it's kit it will be even better.

I use my magwarden as my main dps source despite having a magblade (created magblade recently and still learning class and rotation). I started with morrowind and made a warden and kinda just got used to it. I personally enjoy being a warden, and I have amazing self heals and great sustain with the netch. Sure, the dps isn't nearly as good as most classes, but I can hold my own very well. I do dungeons and trials all the time with my warden with little issues or complaints. Like others have stated the lack of cc or certain group synergies are things that need addressed by ZOS.