As always, the WoW expansion will bring people back but the current state of the game is unfortunately suffering from the same problem it always has: releasing a final tier and dragging it on for absurd amounts of time. That's probably going to happen again and again but, as always, it rarely deters people from coming back. My guild just went on break from raiding until 6.0 but that still seems so far off. I guess that's a testament to how much MoP has dragged on.
It really depends on what you're looking for. I've put a lot more hours into ESO than when I created this thread and I feel like it's better the farther you get. The introductory content is a bit more plain than the stuff you get into, but once you're waist-deep into the game there is definitely a lot to do. I think it would depend on how the combat appeals to you. Starts slow, again, but once you have a lot more choices your builds can get quite interesting. You can have two bars of 5 abilities + 1 ultimate at a given time but it's a fluid system where you can swap bars/weapons in-combat and change your bars at any time for free, on the fly, depending on the situation. For example, if you spend your skill points (of which there are many) the right way, you can literally switch between full DPS and full effective healing on the fly in combat. I really like the flexibility in how you can build your character.
I'd look up some level 20+ dungeon videos and see how those aspects appeal to you. The bosses, combat, dodging, and all that happy stuff. Even if you weren't heavy into PvP in other MMOs, I still maintain that Cyrodil is a stellar zone. It's the one-stop PvP zone that's bigger than several zones put together. Many castles, keeps, resources, and siege weapons at your disposal as 3 factions can fight it out. What impressed me more about that zone was the unscripted PvE you can find there. In true Elder Scrolls fashion, you can wander around and find delves (public dungeons), towns, quest hubs, and all that within the PvP area itself. It's that big.
This could be a decent time to go over what they announced for their first content update: Craglorn. It's something called an adventure zone which we now know is a full-fledged max level zone they add to the game. Only wrinkle in that is all the content, public dungeons and quests included, are for groups of 4 players. The public dungeons here are actually instanced to your group though, but they're more like mini dungeons akin to the normal stuff you would discover while playing solo, only tuned up for a full group.
Coming with the update is also the first raid, a 12-person Trial in Craglorn. As always, there are loot drops from bosses and exclusive items to be found there, but all Trials are also timed so once you have it down, you can push to clear it faster to move up the leaderboards. There's supposed to be some kinds of bonuses associated with that, a bit of incentive to keep repeating the content weekly aside from loot. The other tidbit they revealed was that there would be a group-total limit on how many resurrections can happen to pass the Trial. That might seem rough but this particular piece of content is only designed to take a couple hours tops to clear so it's more for the competition of learning it then really getting it on farm.
Seems pretty interesting for a first update but that's what's down the pipeline. Otherwise, at max level, you continue to earn Veteran Ranks which are like levels and are actually required to equip certain higher levels of crafted gear. There are Veteran Rank dungeons (heroics, basically) as well as the opportunity to continue questing in the other factions' territories, tuned up to in difficulty for level 50s only. I would say there's a lot to do at the moment but we'll have to see how well they keep things fresh and what kind of content they add. The Q&A said not all updates will be Trials or Adventure Zones, but they have a lot of things in mind such as adding stuff like the Dark Brotherhood or Thieves Guild and some solo-oriented stuff. Time will tell but I can give a positive review at least from my perspective.