The game may be flawed and trying to 100% the game is tedious. However, the gameplay is fun and it is fun choosing your adventure as you play the game. You could side with the heroes, Black Doom's alien forces, or just speed run to the end of the level to go neutral.
I know this game was criticized for using guns in a "Sonic Game," but the gun mechanics are actually fun to use. Is it silly, yes. Does it make sense in a Sonic Game, probably not. But this game is about Shadow the Hedgehog. He isn't Sonic, and that what makes him cool. I want this game to be preserved, not just as a time capsule of the era this game came out, but also as a way for modders to make this game more interesting.
BTW GameCube supremacy all the way!