Sorry. I was really debating whether or not to post it, but I really didn't want to pass up the opportunity to make that remark.
As to your actual question, sadly I don't know. I haven't played Sonic Generations on PC, so I don't know how it's supposed to look. If you say all of your other games play fine, it could just be an issue with that game. I guess I really don't know how bad it looks for you, but it's possible that that's how the game runs on PC. --- No one man should have all that power.