While the objective of this boss wasn't so special (avoid Chaos' attacks, collect rings, and maintain enough speed to smash into his brain), the post-apocalyptic setting that this boss battle took place in was cool and edgy for a Sonic game. Also, bonus points for having such a cool name for Sonic Adventure's final boss. Unfortunately, Perfect Chaos doesn't rank higher on this list due to Sonic Adventure's clunky controls and the switch from the game's cool theme song to boring orchestrated music half way through the fight, both of which detracted from the atmosphere of the boss battle.



Screenshot sources:

Cut scene Chaos

In-game Chaos