I've played a lot of different games, but for the most part, I just lose interest when the game forces you to return each day. For example, if you didn't keep coming back to farmville, your crops would die. I don't like games that require that kind of investment. There are a few good ones I'm playing now, but the one I've stuck with since I discovered it is Castle Age. It's a simple fantasy style questing/fighting game that doesn't penalize you if you don't have time to play it every day (or 800 friends to invite).