two things really drawed my attention,
- Character costumization (I don't know why it took so much time to someone implement a costumisation system like "The sims" or "Oblivion" into a MMORPG, I guess that 5 years from now we will laugh at old online games because everyone looked the same)
- Flying (Freedom of coming and going always atracted me in a game, that's why I love GTA)