Sonic and Knuckles is the second half of Sonic the Hedgehog 3, thus it's the good half and is awesome!
It uses lock-on technology to allow it to become an expansion of both its other half but also Sonic 2, allowing you to play as Knuckles in that game.
Same as Sonic 3 but with some diffrences, including being able to play as Knuckles.
While it's not good, it's not bad either. it's pretty awesome it even released at all.
Review scores average out to be "Not Bad."