Honestly speaking, I think this will probably be the most inspired Sonic title we've had in a long while. What I'm seeing here is a lot of unique environments as well as plenty of unusual gimmicks provided by the wisp that not only keeps the gameplay fresh, but fits in the realm of what Sonic is all about: physics, speed, and crazy-ass visual spectacles. On an artistic and stylistic approach, Colors definitely looks more appealing any other Sonic game made in recent history.
How fun this will be still depends on other factors, such as level design and game progression. I've never been a huge fan of the usual Sonic boost that's appeared in Rush and Unleashed, and one of my concerns is that it'll be too easy to use and make the game relatively unchallenging, as it usually seems to do.