Second the avoidance of WoW. It kills brain cells more than anything. I did a free trial of WoW once to satisfy my curiosity, but found it too cartoony and childish seeming, and not very fulfilling in terms of exploration and discovery or tactics, which were the things I enjoyed about MMOs.
If I went back to an MMO that currently (still) exists, it would probably be EQ2 or CoH. EQ2 has an art style that really appealed to me and even though it was zoned everything was set up in such a way that it was still very exploration friendly. It's not nearly as simplistic as WoW in gameplay, either. CoH because at the time it was the best at up-front appearance customization and superhero gaming (Champions Online looks like it might do better in both respects, though.)
EQ2 would be more appealing to old school D&D players, I think, whereas WoW seems optimized for old school Mountain Dew swilling Diablo players.
Of the new games coming out, Champions seems interesting. From the developer's comments and blogs it sounds like it might be good.
I followed the news of Star Trek Online for a while, although STO looks as though it could follow in the footsteps of Star Wars Galaxies all too easily. As details of design and implementation become clear, it seems less appealing than the initial hype and the great ideas the fan base was coming up with for intelligent roleplay. For a while I thought I might get an MMO with a compelling skill system, and get to play a character whose sole focus was exploration and puzzle/problem solving (ie, an engineer or science officer.) Instead of taking the game in that direction and having a guaranteed fanbase of Trekkers and roleplayers, they seem to think shooting phasers, blowing things up, and simplified gameplay is the better way to go to compete with WoW. Why does every development team try to be the next WoW? (This is another reason why I can't stand that game. I've seen more a ton of good ideas thrown out the window by developers trying to crack the WoW ceiling, to try and get mass market appeal, and failing miserably. WoW created a culture of greed among MMO developers that has killed a lot of good concepts.)
Odds are good they'll throw their loyal fanbase under the bus to try to get mass market appeal. I wouldn't bet anything against it happening because to some degree it looks like they've already done just that.
On the various games out there, I'd read up on the following if you want some interesting MMO history:
The original Everquest, from which a lot of the standards of MMO gaming (especially MMO fantasy gaming) were derived. A point of interest that might help understand the design of game mechanics better includes "the nerf" - typically, the practice of weakening a whole class or build option in the name of balance because one ability might be too good, instead of just fixing that one ability. Sadly, game designers still do this. (See the Star Pact Warlock in 4e.)
Star Wars Galaxies. The ever-sinking Titantic of MMOs. It's always interesting to get opinions and different versions of how LucasArts pushed the game out before it was done (a recurring theme with their games), then the developers continually screwed with the game mechanics, and then continually screwed with their fans. This game was like the Jurassic Park of MMO design... with everybody in the role of JP's chaos theory scientist "everything that can go wrong" character Malcolm, criticizing the developers' lack of foresight or comprehension as everything went wrong. If there were a textbook of what not to do in game design, this game should be part of its focus. If there was a textbook on how licensed products can be screwed up by interference from the license holder, then LucasArts need be the only subject.