I'd say this is the game with the most mixed opinion that I've seen. All 5 characters are the same from Advance 2, and now they are all doing a partner system similar to Knuckles' Chaotix. Each character can be paired with another character and each main/partner combo has its own special abilities and qualities. You can check the Sonic Wikia for what each team combo is capable of. Otherwise its going to be very trial and error. Say Sonic for example, in some teams he has his insta-shield, in some he has the bounce attack, in some he has mid-air attacks and moves. But you won't know until you pair them off and play. In a way that's AWESOME fun and on your first playthrough, it probably will be. But in later levels you may want to build a team that has abilities that make tackling certain stages easier so knowing what qualities each team comination brings will be very handle when trying to be effiecient. The special stages are STILL a major pain in the ass to get to. But at least the special stages here is probably the easiest in the trilogy. But still kinda hard though. The game has a lot of bottomless pits/crushing areas so be careful with that. This game, has a lot of Sonic CD like exploration, especially when you're searching for the various chao in the stages to get access to the special stages. I really like the game, especially the whole partner system. Thumbs up in my book, but approach with caution as its pretty polarizing for many.
This was the first Sonic game I'd ever played when i was a kid. Such Nostalgia