So, as far as it looks, this game isn't as good as I hoped it would be (great, the streak for awesome games [starting at Sonic Generations] just ended). Fortunately, as far as the review goes, it wasn't completely and terribly awful, either. It was just... "ok."
Scarred Sun, the reviewer of the game on Retro, said that the levels were bland, most of them being uninteresting and unoriginal (how many times have I seen that word in a SEGA game?... they need some ideas), there were still very minor issues with physics (not big issues, though; most of it was fixed), and the music was "underwhelming", saying it just might be the worst soundtrack for any Sonic game. She said that "it really is a shame, because there are remixes and arrangements of the songs done by fans that really show the songs in a better light–I just wish the release had those instead." Ouch.
Scarred Sun said that they didn't pay enough attention to the level designs and all because they were so concerned about correcting the physics. So was correcting the physics a bad thing? Most certainly not. But it's like a game of capture the flag. You can't have your eyes on one person and try to tag that one person without keeping an eye on someone else trying to grab your flag. It's the same here. You can't keep your focus on one thing and then not keep your focus on another important thing. You have to focus on everything in the game and make sure everything is the way it should be. This is why it's "Sonic Team". You need a team. Everyone plays their own part, but no one can do the part poorly (especially if they know they can do much better), or it's assured that that part of the game (whatever it is) will be poor.
So, stating all of that, it sounds like this isn't a very good game. But there are a couple of good things. For one, Scarred Sun said that "the final boss of the game ... may in fact be one of my favorite Sonic the Hedgehog series boss fights, which came as a great surprise. It hits a lot of sweet spots and actually utilizes the strengths of Sonic 4 in the best way possible. It’s a shame the rest of the game didn’t receive the same amount of love and care that this obviously did." Indeed. You see? They pay too much attention to one thing and... oh, you've already heard me talk about this.
So there you have it. Retro's review and my feedback. Hope this helps.