I'm about 2.5 hours in now. It's basically Sonic meets Super Mario Galaxy, as the trailers may suggest. The blend works pretty well IMO, although it does lead to a few levels that feel overly "busy" due to cylindrical platforms with things going on on all 360 degrees of them. It has the standard gotta-go-fast running and jumping of most Sonic games, but makes a few control changes that take some getting used to:
- Sonic has a double-jump like he did in Sonic Colors, but the second jump takes him out of his spin, leaving him vulnerable. This makes double-jumping a risk-versus-reward situation as you can get significantly more height at the cost of being exposed to attack.
- The homing attack is on a separate button from double-jumping and has a couple variations: the standard one (A button, which also works as a jump), which now has a "chaining" ability that lets you home in on multiple enemies and attack them automatically in sequence when pressing the attack button (a couple levels make very cool use of this as a way of getting across pits or scoring massive amounts of points - the score for defeating an enemy doubles for each successive enemy in a chain up to 3200 points), and a kick attack (X button) which only works on certain enemies, but will send them flying into other enemies if it connects.
- The return of the spin-dash to 3D Sonic is an interesting choice. I don't find myself using it very much outside of the 2D levels though.
- Running is bound to the RZ button, with Sonic's default movement speed being notably slower and allowing for more precise platforming without accidentally taking off into a pit with the slightest nudge of the control stick. I hold down the run button most of the time out of habit, but the slower speed is immensely helpful in many of the 3D levels. Holding down the run button while standing still allows you to do a charge-up similar to the Super Peel-Out (figure-8-legs charge-up thing) from Sonic CD.
The changes, while daunting in their sheer quantity, seem to be for the better. Like I said though, it takes some getting used to as the control scheme isn't 100% intuitive at first.
The game itself is structured similarly to the old Genesis titles, with each area consisting of four stages, every other one having a boss battle at the end. There is a world map which can be moved through in a hex-grid pattern and includes some side stuff in hexes that aren't occupied by levels, such as bonus games and extra lives. Some stages don't match the theming of the area they're in, but it really doesn't make an impact IMO; if you're expecting a narrative masterpiece out of a Sonic title, you're either unfamiliar with Sonic in general or you're just plain doing it wrong.
Not sure how many areas there are, but I'm guessing it can't be more than seven given the "Deadly Six" villain troupe + Dr. Eggheadmanbotnik.The "Deadly Six Bonus Edition" (which was given to all pre-orders and is also the default for the first batch of games to be shipped out to stores) includes an extra level based on NiGHTS into Dreams, with super-short mini-battles with each of the Deadly Six assisted by bosses from NiGHTS. The whole stage is basically one big string of references, so if you haven't played NiGHTS you probably won't understand most of it, but if you have, it's well worth a try. It doesn't cost any extra to get the Bonus Edition right now.
In short: it seems like a solid game, although it might be on the short side (I don't know how many levels there are exactly, but I get the feeling I may be about halfway through after 12 stages), and the changes to the controls take some getting used to. The SMG-esque levels might be seen as overly gimmicky by some, but I personally think they're nice; I wanted more SMG-type action after SMG2, and this game delivers. It's good enough to make me want to try the 3DS version once I get some extra cash.
The reviews are probably not worth listening to. There's a lot of "It's Sonic so it suckz lololololol" out there, and only a handful of reviews that offer any degree of legitimate thoughts on the game itself.