I honestly think, that although the Adventure games have their fair share of trouble, they still remain the best way to play Sonic in 3D. Make it about platforming, not about speed.
1st Adventure had without a doubt the best general character/stage setup. Sonic was the obvious focus, by far the longest quest, and at the same time Tails and Amy played reasonably similarly (not to mention Tails, you know, WAS PLAYABLE). The gimmick character quests were kept short. Problem was, the game engine was buggy as hell.
Sonic Adventure 2 was most definitely better polished, but made the action an even split between Sonic, Knuckles, and the sick Gamma-derivative that they decided to make Tails into. Nevetheless, it is definitely my most replayed 3D Sonic, and IMHO features some of the best stages I've seen in 3D platforming (Final Rush is simply epic).
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