This game is the first Sonic game to have a multiple ending system and it is also the first game being aimed at adults instead of childrens.
This game also has many kickass musics.
The gameplay is a hit or miss to me, personally the gameplay was fun even though it was a bit broken.
The game has a few glitches and some AI problems, that's pretty much why I give it a 7/10 instead of 9/10. The other problem of this game that makes it not get a 10/10 is that sometimes it is kinda repetitive.
I recommend it, but if you are interested into the franchise you should start off with Sonic 3 and knuckles, Sonic CD, Sonic Mania or Sonic generations (for a more modern gameplay).