The Sonic series is one that never grabbed me. I have played the demo for this game (while it was available as it was a dated demo) and for me I was getting a headache, this is probably the first game that has ever done that to me.
The problem was my eyes couldn't really distinguish well the foreground from the background and kept changing focus making it hard for me to play it. So that isn't a good sign for me.
I honestly don't know why this franchise is so loved, simply because SEGA has seem to do everything possible to turn people off with game after game being bad and forgettable. I really hope this game lives up to expectations for you and that it is well made.
With games like Skyrim, Assassin's Creed and Uncharted coming out IDK how well it will sell.