Sonic Unleashed has been brought to PC thanks to intrepid modders. My first question was "why?" but now it's "how?" as the game doesn't exist on the PC format. it's simple: they modded Sonic Generations to make it run silly. No wait, that's not simple at all.
It's essentially the best - if not incomplete - version of the game money can't buy, because it's free. You can download it here, but be warned, you need a Steam version of Sonic Generations installed for it to run.
Here's some footage of the mod in action:
What do you think?