Here's my two cents.
Is it a great game? Yes.
But is it worthy of being the sucessor to 3&K? It's hard to say.
Don't get me wrong, this is the first time Sonic Team has done something right in a looooonnng time, and this game is great in it's own right. But let's just pretend that the game was for the megadrive. PHYSICS ASIDE Sure the graphics would look great and the homing attack will work wonders, but I would seriously doubtthat anyone will think it's that good. Sonic 3&K is my most favorite sonic game of all time, and people seem to forget what new things it brought to the table (sonic's Instashield/Barrier powers for example) and as for Sonic 4, Barely anything new and innovative was introduced. I know alot have happened inbetween Sonic 3 and 4, resulting in very little wiggle room in terms of scamatics (which kind of lowered my expectations a bit), but I was expecting something spectacular. I was suprised how much was rehashed in this game. For example, the special stages came straight out of sonic 1. Now, I know that Sega is experimenting in the first installment and don't want to try anything new, yet. But, this seems more like Sonic Nostalgia other than Sonic 4. Even most of the Eggman battles were rehashed straight from sonic 1&2.
Now I heard that SEGA searched the forums of popular sonic fansite to see what would they would want in a Sonic game. That's the problem. OF COURSE they would want another sonic 2. The thing is that most of the time, fanboys don't know what they want (yes, I'm aware that I'm talking about myself in this matter), they look back at something relevant that they liked and they want more of that. Having more of the same thing does not a good sequal make. Do you think after sonic 1, the fans are like, "This game is good, but do you know what would make the game better? If sonic had a sidekick, who is a faox with two tails, and who can fly!" ? Of course fanboys won't say that. Even though Tails was useless in Sonic 2, he still was a great addition to the franchise and SEGA made it even better when you were able to control him in Sonic 3 and he could discover differ paths in the level.
I'm just rambling on, here.
But, basically, although I don't think it's nearly as good as the first three, it's still a good game. But with four stages with most of them being rehashes, and for $15? Though I played it on my friend's wii, should I download it myself?
I know going back to the fundementals is a good remedy for these shitty sonic games, but releasing a copy of those games will not bring Sonic back to his former glory. Nowadays, I just think people are getting desparate.