Reviewers gave this game 8's, 8.5's and 9's but the majority of us would agree its not a great game because of the repetition and padding. Imagine how many people bought it.
Giant Bomb's Ryan Davis (rip, but lets be honest) gave AC3 a 4-star review and then went on radio to say the game was a "hot pile of s**t". He pretty much represented a lot of reviewers in this regard.
"This game is full of issues, but it's Assassin's Creed, so 8"
This is why people are so angry that Mario Kart 8 and The Last of Us got 8's. People are wondering whether GS really thought they were essential experiences or they were obligatory-8's.