Also fan-favourite Metal Sonic appears as a boss near the end.
Likely the reason Knuckles is in the game.
Even Better Sequel: The game takes what Sonic Chaos did right and makes it even better than ever. The graphics are some of the best on the Game Gear, the level design is much more elaborate and fun, and the boss fights are just the right level of challenge for a fast paced game.
Funny Moments: The final fight against Nack the Weasel in Special Stage 5. He's in a drill machine, and once you hit him enough, he'll fall and his drill will get stuck in the ground. You have to bash him all the way into the floor in order to truly defeat him.
That One Level: While Tidal Plant is one of the more bearable underwater levels in the series, Act 2 has some irritating spots where there's a serious dearth of air bubbles, making it very easy to drown if you slip up, waste time or avoid using the giant air bubbles you can travel in.
Special Stage 5 is also very annoying due to some puzzle elements thrown in, namely throwing in several bottomless pits that are very easy to fall into unless you take the right path and don't spin or jump into it (because that will destroy the fragile platform below you) and then there's some platforms up ahead that you can unwittingly destroy if you spin jump onto them instead of using the springs to safely jump onto them and then spin jump off of them. It's very easy to get yourself stuck in it.