Gameplay! I played Ragnarok Online for 4 years and it's 2d. I just love everything about it - from headgears, to homunculus, to jobs, to War of Emperium.
Also with UWO (Uncharted Waters OL), the graphics isn't all that eye candy, but the quests, storyline and pirate-killing feature of the game keep me hooked.
"There are two ways of being happy: We must either diminish our wants or augment our means -- either may do --
the result is the same and it is for each man to decide for himself
and to do that which happens to be easier." ~ Benjamin Franklin