The thing that I hate mainly on meta critic is the in-consistency with reviewers they allow. I actually had them add reviews that were up on Gametrailers to their selection of reviewers, for couple games.
I hate that there's a bunch of site's reviewer's that sound like they are mostly from generic sites, or sites not known to cover video games.
Happens with a lot of game reviews I see on all fronts. They have some Brazilian website or something give a game a 10, and I'v never heard o them.
To me it's the same as joe schmo on rottentomatoes reviewing a film. I see reviews from people who have a blog site and it get's counted.
Big player's to me for reviews, GiantBomb, Gamespot, IGN, Destructoid, Jim sterling, Kotaku, gametrailers, GAME Informer, Digital Spy, The verge, unfortunately Polygon, EGM, Edge, Attack of the fanboy, Rock Paper Shotgun, can't think of any others off the top of my head.
On a side note how does an expansion for a Multiplat game get a higher review than an Exclusive, that's made from Previous Halo developers?
EDIT: Forgot Games radar, Eurogamer