Facts :
Metas are the most reliable indication of a game's quality. It has its' flaws but there is simply no better indicator than it. It is the aggregation of professional reviews, what else ?
GT5 is quality-wise the declining point of a series, metas might have been lowered due to the difference between the expected and the delivered, but in all honesty, the PS3 crowd has to choose :
Either uberhyping increases metas (due to the rolling tsunami of marketing versus little underpowered journalists) or uberhyping games hurt the sales (due to this very same difference between the expected and the delivered and the egocentric reviewer who decides the game must be punished).
But it certainly cannot be both - and it certainly cannot systematically be the one which better suits PS3's interests - typical example of this double standard : Halo's meta has been hightened due to over-hype / GT5's has been lowered due to over-hype)
And please oh please the "you have to play it to understand the value of a game" is the worst argument ever. Every-single bad game has had a fan (- maybe not the really bad onees as the ET games in the early 80's, although who knows ?), a fab of a bad game who would tell you it's great, especially at about 75% of its' completion.
