Now this technically isn't a proper post on the topic because it's not about free music, but all about the score of a commercial video game (even though the score itself was never released), but I'd just like to demonstrate in a good example how extremely the quality can vary between different tracks from THE SAME COMMERCIAL PROJECT.
The talk is about the (now long closed) MMORPG The Matrix Online.
Its quality ranged from absolute amazing stunning, distinctive genius stuff like this:
http://www.youtube.com/user/Reboothis#p/u/36/GRo2JKAz44o
http://www.youtube.com/user/Reboothis#p/u/39/x9S-_086BvI
to bland, cheap sounding direct rip-off stuff like this:
http://www.youtube.com/user/Reboothis#p/u/11/Y81suATzTSw
http://www.youtube.com/user/Reboothis#p/u/18/4d1XPvMhfL4
or plain old boring-ass uninteresting "fighting" tracks like this:
http://www.youtube.com/user/Reboothis#p/u/1/HpXO6kdgmrE
or actually pretty cool ones like this:
http://www.youtube.com/user/Reboothis#p/u/32/DCSxqixDOlU
Again, music "written" and produced for THE SAME GAME, afaik by the same people, and yet one sounds like inventive, originally produced "ambient" music kicking the living shit out of quite a few "meditation albums" out there, while the other sounds like a kid typed some of the movie score in his Guitar Pro at home.