I find that when I'm in that mood it's best to shut my brain off and not think too much about what I'm playing, or I just go with something I know I'll like. It's good to own a few easy to pick and play arcade games, Counter-Strike, Team Fortress 2, Bejeweled, Diner Dash, Tetris, or basically anything that costs less than $20.
I mean sometimes playing games that require you to think sucks.