Undoubtedly one of the most brilliantly conceived puzzle games of all time. The only thing holding me back from 5 stars is that Portal 2 managed to deliver an even greater experience with a fantastic narrative to boot.
I'm biased as I come from Super Smash Bros. Melee but I really miss the super deep tech and movement options that the GameCube iteration of this series provides. Of course the game is polished to perfection though so this comes down to personal preference.
It's undoubtedly a technical masterpiece and I'm sure the story is fantastic as it is set up really well, but I just couldn't get past the movement & actions all feeling very slow. Maybe one to pick up another time though.