I usually play multiplayer games, so I can't judge too many games' soundtracks, but usually they were good enough for me. :) Lord of the Rings Online and L4D have awesome music, so no need to have MP3s playing in the background. When I play competitive titles, like TF2 or CoD4, I prefer to keep to the in-game sounds, as it's important to hear what's going on around you and keep track of your surroundings. :)