One of the biggest hits on the Genesis was Sonic & Knuckles. It was also the first (and only) Genesis game to have backwards compatability. With that technology, you could "lock-on" the Sonic 3 and Sonic 2 carts to play Knuckles in those games. Or you could lock on Sonic 1 or Sonic Spinball to play special stages.
Anyway, I'm getting off topic. This game is a follow-up to the events in Sonic 3. You play as either Sonic or Knuckles. In Sonic's game, you help Sonic continue his fight against Robotnik in one more attempt to destroy the Death Egg for good. In Knuckles' game, you try to find out who's stealing the Chaos Emeralds. There are eight zones to explore, each two acts long. There's a mini-boss at the end of act 1 and Robotnik at the end of act 2. There are 3D special stages just like the ones in Sonic 3, but they're harder.
Like Sonic 3, the game is a drag alone. The zones are fun, but it's cooler with Sonic 3 and Sonic 2.
Strategy | Secrets