The game that finally and completely opened my eyes to the problems that reviews can have was FIFA 10. It got praise across the board, it was described as the best football game of all time, and yet, on it's release weekend, the official forums were full of complaints. The games main single player mode, the 'Manager Mode' was full of bugs. By the end of the weekend, a list of ~70 major bugs with the game was created by users (most of these were never fixed, but that's something for another thread).
It ranged from players disappearing from your squad list, only to find them playing for someone else, to suddenly having a transfer budget of negative £xxxmillion, no matter who you're playing as, or getting fired because your lowly team 'only' managed a draw away from home to Manchester United and you're sat in third place in the league.
Questions were asked in review articles. If the players could spot these massive problems in one weekend of play, why did nobody mention it in their review? And I mean that, not one magazine or website mentioned these problems even in passing.
Ultimately, I realised why. They have a lot to get through, so with football games, it's easy to judge how well it plays by simply playing exhibition mode, as that will show you how the game actually plays in a match. You don't really have to touch any other mode, you can just rely on the press release to describe any new additions, and give it a score based on your few minutes with the most unimportant mode in the game...