Eve pretty much has a monopoly on the 'good MMO' subgenre.
Yeah... EvE and WoW are basically the only two remaining 'good' (Wow never caught on for me...) subscription based MMO's. EvE is as complex as you want it to be. I know people who use it as nothing but a way to relax at the end of the day, as basically a interactive wallpaper. And I know people that go extremely hard and sink their entire life into it. And both playstyles are equally valid. Probably the best thing about EvE is you don't even have to be online to 'level up' as everyone's 'XP bars' tick all the time, no matter if you're off or online, at the same rate*. It takes about two months I'd say for it to really bite you. Depends on who you play with really. EvE is also the last 'social' MMO in that respect. You NEED people you can trust and depend on to do high level stuff. Things like controlling space, living off the grid, can't be done as solo activities*. And you can't just queue with random mouth breathers to do that. Because of EvE's ruthlessness and difficulty, you need people who will watch your back, not stab you in the back for shits and giggles.
And the world... EvE is played entirely on one server, with no instancing. There are dungeons, in a sense. But players can scan you down, enter those dungeons, and blow you up, with varying penalties depending on what area of space you are in. Also, the entire world is run by players. For example, recently some players recovered the deceased remains of someone who discovered a new threat, but got killed. He managed to broadcast the threat before he died. The players were approached by the in game security force for the remains. They refused to hand them over. So, they will now be engaged by the police force of the game, and have had a bounty put upon them equal to 750 U.S. Dollars. The in game security and such is run by the devs, so instead of forcing them to hand it over, they are allowing this to play out and may take action against their in game guilds.
You can read the full story here. EvE's tagline, "In EvE, the story is not real, until players become a part of it." is completely true. Actions you take have ramifications everywhere. It's not like WoW, where you can slay the boss that wants to destroy the world once, and then he's back, threatening the same exact shit, as if nothing happens. For a smaller example,
yesterday, one of my ships got blown up. That ship, and all of the stuff on it, was built by players. It's also gone forever, and everything in red in that message. I don't get it magically regenerated. If I want to fly it again, I have to go out and buy a new one, also built by players. No other MMO is like that. EvE is not a theme park you can stroll your way through. As cliche as it sounds, EvE is real.