So yeah. I'm gonna copy Gavin up there.
SA1 and SA2: Meh. Didn't like the music all that much. It Doesn't Matter, and a couple stage songs were alright.
Heroes: I can agree with just about anyone that the theme was terrible, but We Can, This Machine, Team Chaotix, not to mention NUMEROUS stage songs were golden.
Shadow: Not sure about stage music, but the themes were... alright. Waking up is pretty much the best out of them, and it ain't even all that good.
Sonic Next Gen: ....Nah.
Unleashed: I was impressed with most stage BGMs, but otherwise, eh.
Secret Rings: Other than the main theme, the music is mostly alright. The boss themes sucked, but a few songs like Let the Speed Mend It and White of Sky stood out from the rest.
Black Knight: The remixes were cool, and the stage music is pretty sweet, but my favorite is definetely Live Life. It kinda reminds me of that old rock from like the 80s and stuff.
Colors: HIGH EXPECTATIONS MY FRIEND. HIGH.