Let's see, over the last 7-8 years, I've played:
City of Heroes
DC Universe
EverQuest 2
WoW
Rift
The Secret World
SWTOR
The Matrix Online
Lineage 2
Tera
Second Life
Out of all of them, I hated DC Universe (the screen layouts and design) and TMO (the gameplay).
EQ2, as the "old-timer," seemed pretty cobbled together, but it deserves a nod for being one of the first really big game and precursor to WoW.
WoW of course did do an excellent job revamping and packaging MMOs for entry-level players and still controls market share; they basically created the Second Generation (or third, depending on how you number them) of MMOs.
I will always have a soft spot for CoH, since it was my first MMO, and the first one where I maxed out a toon (my kinetics/fire controller, BEFORE it got a rep as Flavor of the Month). I was very sad when they announced they'd be shutting it down at the end of November this year.
SWTOR was cool because of Jedi and the morality system, but quickly just started to feel like WoW with sci-fi elements, and I got bored by level 20.
The Secret World actually was the most different game I've played -- the graphics, unfortunately, are outdated, but the setting is creepy (kind of harkening back to Quake and FEAR and other spooky computer games), and it uses this really cool system called a Skills wheel, where you cobble together your character completely from scratch, and as you fill out certain parts of the wheel or purchase the right skills to match a particular profession, you gain extra abilities. It also demands that you use the Internet to answer some of the puzzles -- you need to use your head and Google stuff to find out the answers. This can be both fun AND frustrating, since the answers are not necessarily inherent to the game; however, there's enough players out there that you can also just Google the quest name and cheat, if need be. If only the graphics were better, and more cards/professions were available to you based on faction, it would be really good; it wins hands-down on tone if you are into spooky crap.
I think Rift actually is my favorite MMO right now, and I'd be playing it if I wasn't broke. It's of course got similarities to Wow, but introduced the idea of the PUG Raid, and beautifully. When rifts open, you can just run in, you are assigned to groups, and you can just beat the crap out of stuff and ride around with your PUG without ever even talking to them, until the Raid Event ends, and just bail. They merge small groups into one large raid group automatically as well. Overall, they took the WoW concept and built on it, even if it's still generally the same game. I'm a casual but committed solo player, so I really appreciate being able to Raid without having to commit lots of time to a guild, hours on a specific raid, and have to play my part exactly right so that we win; that's just too machine-like for me, and not a lot of fun.
Tera looked beautiful (anime style graphics and play), but... around level 12-14 the character dev and gameplay started to suck. It was all cluttered, the monsters got too hard for soloing in spots, etc. It was a beautiful-looking but "bad" game.
I just started playing Aion, which is a free NCSoft game, and I really really like it. I would say it's equivalent to some kind of mix between WoW and EQ2, in design, yet it's entirely free. And you can fly (on a limited basis), and sometimes need to in order to finish quests. I haven't had an issue in figuring out what to do, how to build my attack chains, etc. Definitely something Tera needs to figure out.
I haven't gone into Second Life for years now. I was in there a lot for about a year (in the mid-2000's), especially in regard to being able to make and sell your own items and get money back OUT of the game. There was a killing to be made early on; unfortunately, it seemed like the economy broke at some point, especially for the adult industry (where I was under the impression you could make a lot of decent money doing chat sex, until the webcam chicks came in and shot everyone in both feet by doing webcam with less talent and far cheaper... and much cheaper than they would be paid IRL webcam business... stupid).
EDIT: Wondering if NCSoft pulled CoH to focus on other games, like this one:
http://us.bladeandsoul.com/en/
I'm a "customization and exploration" player, as well as primarily a soloer. So if I can design my character in unique fashion and she looks cool, then that's part of what I like in a game. (Also has to have decent solo play as well as ability to team up easily.) Asian games typically do "look better" than western games.