Very atypical level design for a sonic game which is a turnoff for a lot of people who end up finding it frustrating, combined with a bit of a higher mechanical skill recquired to do well (properly taking advantage of the unique tech and mechanics of each partner combo) can make it a lot harder to get into.
That and the horrible chaos emerald hunting system, still better than sonic advance 2 in that regard.
Can't blame anyone for not liking it, but its probably my favorite 2D sonic game.
None of this game's ideas deserve to lay abandoned on the Game Boy Advance. It's very refreshing to go back to a game that dared to experiment with the Classic Sonic formula. Partner combos, skill swapping, and the boost mode. It was too much for a regular player to adapt to on a first playthrough and changing the way these characters handle didn't help. They are all stiffer on the ground and super loose in the air. I got used to it after a second replay but there was simply no reason to change that of all things. Collision is this game's second biggest flaw as it is less refined than in the first two Advance games. It's most frequent with moving blocks and boss fights. I really wish they gave this partner combo/skill swap mechanic a second shot. By this point, we had two distinct directions 2D Sonic could pursue and Dimps chose the boost.
That and the horrible chaos emerald hunting system, still better than sonic advance 2 in that regard.
Can't blame anyone for not liking it, but its probably my favorite 2D sonic game.