EVE Online sports a great set of killer attributes, but has a few bits that keep it from the prime-time.
The truly shocking part of EVE is its tendency to break free of the deterministic gameplay that is associated with most math-intensive titles. Due to the player element of EVE, anything can happen at any time. The EVE universe is fairly well split into two groups: the chaos-happy PvP junkies and the "leave me alone" carebears. PvP junkies will find EVE to be the best sandbox ever - with actual people in relative abundance you'll never be unable to find a fight. As I am not a carebear, I cannot tell you how much fun EVE is for that kind of player - I shoot them for fun and I think that what they do is boring.
EVE's crown, however, is in the technology. EVE runs on a single server cluster, so there is no issue trying to find your friends on another server. You're all right there, in one big sandbox. If you're there for the human experience, EVE is your dream-game.
EVE has a few bits that keep it from true glory, and this is all in the department of user interface. EVE is a very esoteric game (Steve Jobs would use his catch phrase ad naseum on EVE) and, as one reviewer put it, "The interface couldn't be less intuitive if it were at the bottom of a f**** well!" I tend to agree.
The learning curve for EVE is comparatively long compared to other games. It takes around four hours to get into the point where you're not longer fighting the user interface, and another week until you're reasonably comfortable with the whole game.
Add another year to become a seasoned PvP grandmaster, if you go the fast track.
Overall EVE has an excellent retention time. Characters dating back to the private beta tests are not all too uncommon, and players who have already trained all the skills they want keep playing for the pure fun of being with friends.
If you can only play one MMO at a time - like me - then EVE Online is a very strong contender. Despite its complexity and learning curve, it still maintains a powerful force in the lineup as the best single-shard MMO with the most convincing, open-ended gameplay around.
You would do yourself a dis-service to disregard EVE Online. I mean c'mon, it's internet spaceships! It's serious freakin business!