My guilty pleasure game would have to be..... Animal Crossing. I mean I love that game to death. It's kinda like the Sims, but you play with cute little animal character neighbors. But your character in the beginning of the game is a cartoony looking human. Plus the game never ends, so you can play it as long as you want.
A great thing about it is you don't even have any objectives, so it's basically free room. Oh, and every Sunday morning at eight, a guitar playing dog named KK would play music at the museum coffee shop. If you sat down and listened he'd give you a CD, so you could play it at your house.
I first became obsessed with this game when it came out for GameCube. I remember when I was a little kid that if I had extra time before school, my grandmother would let me play it. That's basically how I became obsessed with it. You can never beat a classic game system like GameCube.