You have to look different at those ratings indeed. It's not because it had a 7 or a even a 6 it is a bad game. You have to first look into the game, I don't like shooting games for instance, they are too simple and mostly sell because they have a expensive engine that shows some graphics. So even if it gets a 9 i would probably not even try it, M-maybe if it gets a 9.5 i would consider it.
On the other hand i like point-and-click strategy games, you have another code. It got 7 or 8, and indeed the game is not memorable but it was nice and fun to play. Aka worth the money.
This showing that rating don't make games good or bad, but people do. If you don't like the genre you probably won't like the game neither. Thats why i hate the hype thing, games that are meant to be just good are thrown around as ammo for a 'this thing rocks' wether the thing is an engine or console. Leaving people with too high anticipations and thus resulting in an unhappy consumer. This has happend especially in the PS3 branding, games like resistance or lair end up (or will end up) as something considered a bad game. Not that they are bad, people just expected too much of it.
So rating tend to follow the hype, yet hardly live up to it. For example "majora's mask" was sometimes better rated then "ocarina of time", but we both know what game made it to the best titles ever. Yet in the early times reviews were made to distinct immoral bad games from playable games. Just because the hardware and experience could not follow the idea.
Currently it is impossible to make such an immoral bad game. Everyone with basic knowledge can make a game with flash that has recognizable graphics, some controls and nice music. Ten years ago you could buy games that made your ears deaf, you could not control or see the difference between an enemy or a door.
Thats why scores are still Music/Graphics/Gameplay/Controls based. yet it's clear that games should be rated as Innovative/Gameplay/Genre specific, so that people that buy a game know what to expect: a game that tries something new or a game that offers a nice old experience.
Like rayman: raving rabbits is a game that tries to innovate trough controls/has mediocre gameplay/wants to be creative minigame collection. And that tells a whole lot more then boring sound/mediocre graphics/funny bunny minigames and nice Wii controls.