I like it because it uses unused stuff from the original games.Plus it has a hand full of cameos from sonic CD. SPOILER WARNING! It has a true ending. It can be unlocked by unlocking Super Sonic.At least it was not made by Seeeeeeeega. It thinks everyone wants to play as Sonic nowadays.
Also the in the "Act 1" of every level seems somehow different... Act 1 and 2 from the original games are smashed together so the player wont know every thing about each zone (and will feel longer) and Act 2 feels different as well.There is also a DLC for it (I have it)The only thing I don't like is you have to start from Act 1 every single time you die on Act 2.Other than that it is great game to play.I also like the mix of old and new. It is worth the 20$