Well, think of it this way. Reviewers are hired because they have a taste for gaming that reflects the whole of the community. Chances are, they've played games longer than you have, and they know HOW a game becomes fun. While this sounds like a simple science, it actually is EXTREMELY complex, and is one of the great paradoxes of design.
That being said, they, like all of us, are humans. That means that they make mistakes. Keep in mind that they only have about a week to play the game before recording their final thoughts, so in a long-term adventure like Mario Sunshine of Sonic the Hedgehog, they aren't able to experience the collect-a-thon fun of those games.