My choices are fairly predictable given the genre they all fall in.

1) Bust A Groove/Bust A Groove 2. Easily some of my favorite game music ever in both games, and they really don't take a ton of effort. The first considerably less than the second, which can take your reactionary senses for a ride at times. Either way, it's like controlling a show more than it is like playing a game, so it definitely takes the edge off a long day.

2)Rez. I regard the last level of Rez as the best final level of any game I've ever played. For having so little to it, overall, it allows so much pleasure in playing it over and over. It probaly isn't healthy overall, but I tend to feel sleepy after playing. Maybe it's the hours I put in, I dunno.

3)Phantom Dust. I'm lucky to be able to hop on XBL and find a good couple of people to face when I get the urge. But when I do get the opportunity, it's always a bright, flashy, and pretty, explosion filled romp. Keyword being Explosions.

4) Space Channel 5/Space Channel 5 part 2. The soundtrack is, once again, the drawing point for this selection. I somehow haven't unlocked everything in both games, and refuse to see exactly what I need to do to get the stuff. (This fact adds lots of replayability to all of my games) Just like BAG 1/2, it's basically an interactive show.

5) Monster Hunter: Freedom. I get to go out and kill various dragons. Also, the following:

And because sometimes you can't be too sure they're dead

Such a quirky game with a nice simple soundtrack that isn't too bad either. Oddly enough, if you put headphones on while playing this game, you get the feeling you've got surround sound going on. It's a really lush aural experience.

Honorable Mentions:
Wipeout: Pure. Pretty and a great soundtrack.
Wrestlemania 2000. The Penultimate wrestling video game.