This is, by far, the best Sonic game since Sonic Adventure 2.
Story:
It's extremely simple. Eggman has built a theme park in space, apparently feeling remorse for his past deeds. Sonic doesn't buy it, so he and Tails go to check it out. They find out that Eggman wants to use Wisps (where the game gets it's name from) to make some laser type thing. That's basically it.
Gameplay:
It's the Daytime stages from Sonic Unleashed, but even more awesome. Now the big game-play feature here are the Wisps. These give you varying power ups, depending on which color wisp you get. They aren't really needed, but help make the game easier. That's how a gimmick should be I think. Also random point of interest you can play as Super Sonic in the regular stages. For you classic Sonic nuts that's a big plus. I mean that's awesome yes, but I never found it a problem that you only used Super Sonic for the last battle.
Graphics:
This is IMO the best looking game on the Wii to date. Everything from the level design, to the character models, hell even the menus look superb. I mean it comes close to the HD versions of Sonic Unleashed. That's impressive for a Wii game.
Sound:
The music is amazing, but this is a Sonic game we're talking about. When you find a Sonic game with bad music let me know. Sega completely changed the voice cast for this game (except for Mike Pollock as Dr. Eggman) and I think these voice actors are FAR superior to the 4Kids actors. All of the voices in this game are very well done, and I was pleasantly surprised when I heard them.
Overall:
If you ask me, Sonic Colors is a fantastic game. You can tell Sega put a lot of work into this game, it's truly spectacular. It's one of the best Wii games this year and the best Sonic game since Sonic Adventure 2.