People can all agree that Sonic Unleashed had some pretty deep lows -- specifically, the Werehog. But the daytime segments in the game showed promise; almost a return to form. These areas of the game, for the unaware, combined Sonic Adventure-like 3D free-running elements alongside more classical, 2D elements from the series' past. It was easily the highlight of that game.
And Sega knows it, which explains why Sonic Colors is pretty much nothing but those portions of gameplay.