I really enjoy little flash internet games. Nice simple ones that work in your browser and that are easy to pick up are the best. I also enjoy physics in a game, anything from the well simulated (GTR2) to the the best object physics I have ever seen (Half Life 2 series). Fantastic Contraption is a game someone told me about that is simple to pick up for a few minutes and it has brilliant object physics. Plus it gets tricky a few levels in. Sounds silly and simple: Build your contraption in the blue box and get the pink thing to the pink box.