Third track is more "Sonic" than the first two, I think. As for Mania, physics look dead on. Changes to Green Hill are interesting. Studiopolis will probably grow on me, but aesthetics currently put me off, and what I see as gimmicks like the popcorn machine and the radio transporter thing. Doesn't fit, imo, but as said, possible it'll grow on me. There are parts of the level I like.
Too early to comment on Not Generations 2 game. I just hope it isn't dark in theme like the trailer suggests to me.