City of Heroes was my first love in MMOs, and the faster pace of movement and enemies completely spoiled me for WoW. I didn't stick with it until the end, as the Incarnate stuff was the sort of endgame that I don't like. (I should never have to memorize what gets done in what order for what reward. Every MMO that tries to make me do that loses me.) But I agree with others that the way NCSoft treated it at the end was awful and I won't forgive them for it even though I wasn't playing at the time.
(To be fair, they also made mistakes like not doing server merges, for the sole reason that two players named FireFreeze03 might run into each other.)
Fortunately some of the aspects of CoH lived on, or were improved upon in DC Universe Online. Which is something I would have mentioned to OP on this topic anyway.
What I need in an MMO these days, what I can't get from WoW or SW:ToR or any traditional button rotation setup, is fast fun combat. DCUO has one of the best combat systems I've seen. Block/Melee/Range is a rock/paper/scissors for outplaying targets in combat (PvE and PvP). Mouse clicks combinations create weapon combos, while numbers 1-6 fire a selection of powers. There's a nice skill curve on build combinations, choice of attacks, timing, position, angles, destructible objects, and other factors.
Unfortunately they lost me about 2 years ago by roughing up their own leveling system in order to add more grind. The game levels to 30 via xp, adding powers and skills along the way. But after 30 you transition seamlessly to gear score to keep leveling (upwards of 100 now.) That's great, but around the 80s you get to a point where practically speaking you need to be 84 to run content marked 82, which gives gear at 83 which you use crafting to modify to 87, so you can run content marked 85. And if you managed to make it through that sentence and remember what I said above, you'll understand why that annoyed me.
Still, a lot of cleverness to DCUO's design and it's worth trying out at least up to 30. (It's F2P to that part and a bit beyond, then you can subscribe or buy DLC packages.) In addition to the combat I also really like how they improved on the Holy Trinity. As City of Heroes introduced Controllers to the world, DCUO improved on that. Healers manage your health bar. Controllers manage your energy bar (in addition to CC stuff of course). Tanks are tanks, and *everyone* is DPS: it's a mode you toggle between DPS and T/H/C so you can solo or fill either role. Other games should totally steal these ideas.
But as I said I moved on. If you're open to a more flexible definition of MMO, try Planetside 2 or Warframe. The former is a hardcore FPS, no auto aim and no PvE. But there's a large world with 1200 players per continent instance, leveling, weapons to earn to generate builds with, and other things an MMO player might like. However I repeat, it's very hardcore PVP. Be prepared for the steepest learning curve of any game I've ever played. Ever.
Warframe on the other hand is a lobby-based MMO. You're a Space Ninja and you start out on your ship and may not see another player for your first few missions (which are an introductory quest). But it makes for easy grouping in 4-person missions (8-player raids being new endgame). Lots and lots of gear to acquire and build with, including 22 different Warframes (comparable to character classes) that you can switch between. It's a blend of first person shooter, with melee combos and 4 powers on each Warframe. And the developers are constantly putting out new content, all free. (If you're familiar with Destiny for console, it's fairly comparable. Except it's on PC as well as both consoles.)
So if your MMO tendencies favor a bit of excitement, I'd definitely check out DCUO, Warframe, and PS2. But I'll warn you that if you do get into them you'll probably be spoiled for all 6-toolbar button-rotation fighting ever again.
