This unofficial project ports back most of Sonic Unleashed's day levels from the Xbox 360 version into Sonic Generations on PC. It also includes any improvements that are deemed as necessary to accomodate to the better control scheme, higher resolution graphics, and a much smoother framerate.
Well done, team!
Fantastic mod. Difficulty level feels a bit higher than generations with certain levels but that's not implicitly a bad thing. There are some random crashes (at ends of levels) and occasional glitches, but if you get over that you get an enjoyable experience with this quality mod.