It is fun to play at times, but inconsistent gameplay and cliche seen-it-all-before aspects lowers its value.
The "daytime" Sonic is really similar of all that has already been seen in the previous console Sonic games, just not as horrible of gameplay. The "nighttime" Sonic levels are very, very cliche and uninspired. They play out just like every other 3D platformer. This whole side of the game doesn't even feel like a Sonic game. The fact that the daytime side of the game is so fast-paced makes the nighttime side of the game feel very slow in comparison.
The daytime levels aren't bad, but they are almost too fast to take in. When the screen switches from behind you to a side view, it is a bit more pleasing to watch. If the whole game was a re-creation of the classic Sonic game, in 2D platformer view that is, and had improved graphics with linear, level-to-level gameplay, it probably would have been a lot better.