Would be perfect, if the controls were smoother.
However, the only reason I am not rating this game a 10 or 9.5 is due to its control system. The game feels very awkward when you first pick it up and even once you are "used" to it, it still feels clunky. In combination with the fact that the gameplay is centered around using those controls to climb massive enemies, that shake you and cause you to lose further control of your character, it is a pretty big weakness.
At the same time, if you can live with the controls, this game should not be missed. It does too many things too well.
Edit: After playing further into the game, I bumped up the score slightly. The later Colossi are more fun and expose the issues with the controls less.