I couldn't give a shit about what rating system you're referring to. No game is flawless or deserves to be docked points if a reviewer believes it to be one of the most outstanding games they have ever played. Yes, the puzzles in single player were a bit easy, but they are really fun to figure out, and you feel a rewarding feeling when you solve them. Since the objective of games is fun, I don't feel the need to dock points for this flaw. Co-op makes up for the lack of difficulty in the single-player campaign, anyway. Brilliant game.