A very fun game first time through, then quickly gets old...
Sonic Adventure 1 and 2 had less levels than Sonic Colors, but in each of them you were given 3 (for Sonic Adventure) or 5 (Sonic Adventure 2) tasks to perform, including finding a hidden item, collecting 100 rings and getting to the end in a very tight time limit. These were all fun, exciting challenges which kept the games going for a very long time. SEGA should have kept with the idea long past Sonic Heroes, the last game which used them (which only had 2 less levels than Sonic Colors.)
SEGA did Sonic Colors right, but next they need to vary things the way they did with their premier 3D Sonic games, add that to a game like Sonic Colors and you have Sonic perfection (PUT THAT INTO CONSIDERATION WHEN AND IF YOU MAKE SONIC ANNIVERSARY SEGA!!!)