Just played it for the first time, and to completion.
While the physics took a bit of getting used to, and I'm annoyed that the "you don't have to use HA" line was a pile of PR bs, it was thoroughly enjoyable.
My biggest problem with the game by far were the air physics. Stop holding the directional button means you stop in middair? No thanks. It made some of the Casino stages pretty awkward.
However, that said, I think I can say with confidence that this is the closest thing since the original trilogy since Sonic & Knuckles. It may not do justice to them, but it's certainly not an insult to them either.
With this as the prologue and starting point, I can only see it getting better.
Last but not least I'd like to praise the stage design, specifically the latter two Zones. They combined quality platforming with speed, it's something Sonic hasn't really done right for a long time. I guess we have S3&K's level designer to thank for that, right?
Oh and, yes, it's short, but Sonic 2 was bloody short too
I'm satisfied for now.
Well done, previously pretty shite Sonic Team.