It was pretty much my No.1 soundtrack of 2011, and, again, I think the_miker will agree
I think he would too.
Sonic Generations' music is pretty much all remixes and arrangements from the entire Sonic series, from the original Sonic the Hedgehog right up to Sonic Colors. Essentially the Sonic Generations OST is the ultimate Sonic arranged album. And if you're curious, the staff roll credits the music/remixes to Jun Senoue, Naofumi Hataya, Kenichi Tokoi, Tomoya Ohtani, Circuit Freq., Cash Cash, Crush 40, Richard Jacques, and Yutaka Minobe. It goes on to list a lot of musicians and performers. Here's a little sample I posted to my VGM blog a while back, a nice jazzy arrangement of Sonic 3's "Data Select" music. Jun did a pretty rockin' remix of Chemical Plant Zone as well.
Of course I'm just talking about the soundtrack to the console version here. The Sonic Generations OST includes the 3DS music as well, which I haven't even heard yet!