It's a pretty fun game but it has a lot of flaws.
first of all, sonic's physics are a mess, it would be better if it was closer to games like sonic adventure 2 or sonic unleashed. second is the inclusion of classic sonic, he was never supposed to be in a modern game outside of generations. and one of the biggest flaws is that you have to play green hill levels a lot, sega has been putting green hill in their games for the last 20 years and it's not even nostalgic anymore, it's just too repetitive.
and the levels are too short, the whole game can be completed in less than 3 hours.
it's really fun to play tho, if those flaws that I mentioned were gone it would be a solid 5/5