I would go as far as to say better then Adventure 1 and 2, but that would bring the old fans here trying to change my opinion, but yeah. Sonic Colors is the best 3D Sonic game I've played, and definitely the best this decade.
Think Sonic Unleashed 2. Speed remains the same - only boost has been lowered. It's pretty much luck if you can boost now. The only way to get boost is to kill an enemy(enemies don't have a 100% chance of giving it) or picking up a white Wisp powerup. The level design is also much better then Unleashed. Your not just holding 1 direction and jumping, you are actively pressing buttons in all directions.
The game's story is decent. It has it's cheesy lines, but I actually found myself giggling a bit over how dumb the jokes are. The only voice actor who didn't get removed was Eggman, and he deserved to stay. Roger Craig Smith(Dude did some RE5 and Valkyrie Chronicles work, IIRC) potrays Sonic the exact way he feels like he should sound like. The only voice actor who I think shouldn't stay for another Sonic game is Tails(Kate Higgins - who also voices Wave in Sonic Free Rider). She made Tails sound from a 4 year old girl to a 8 year old girl with a sore throat. Not that great to hear.
The game has hard moments Some are frusterating to no end, but otherwise the difficulty bar is up there. Doing a no hit run is very difficult.
The final boss is the only part in the game that infuriates me to no end. I've never seen a boss put in a setting more amazing then an elevator on a giant floating amusement park that's blowing up from the inside out. It both amazes me and makes me power off my Wii every Game Over I get from it. It's just really cheap.
While I go on, here are some more downers.
- There is no spindash
- You can jump forever in the water
- Some Wisps are barely used/given(Like the Green Hover)
- There's only 4 "original" bosses. All the other bosses are just somewhat harder versions of the others.
- Bosses die in 2-3 hits if you use the Wisp power. This makes it incredibly easy to kill a boss.
- If you're not going fast, the controls are slippery. They feel chunked, and not responsive. I've tried with the Nunchuck and my Gamecube controller, and both feel shitty if you're not holding a direction.
- Unlocking Super Sonic is confusing. The game offers not one hint on what you're supposed to do. What to do is to collect all the hidden red rings in every stage. The Sonic Simulator(The Metal Sonic head thing on the main map; It's referred to as Gameland ingame) will add a stage to every world there after so many rings. Once you beat all the stages there(which requires you to get all the red rings), you unlock Super Sonic, who has unlimited boost and the likes.The game doesn't even acknowledge Gameland, anyway.
Play Sonic Colors if you have a Wii. Seriously; it has the best graphics on the Wii this year. There are few stages that are just plain junk/boring. For a Sonic game, it's a step in the right direction.