So you admit that the Halo MP is AAA?  But not the whole game?  If a disc comes with a AAA multiplayer, and the driving concept behind the title is multiplayer play, how can you say that a mediocre campaign mode makes it not a AAA title.  That would be like if I said that Uncharted was AAA single player but didn't deserve a single A because it didn't have multiplayer.  I agree the Halo campaigns are shitty, but it's the best MP console shooter of the last two gens, easily.  The campaign is added bonus material.

If you want to use a somewhat objective but very factual approach (rather then a subjective one) you could take a site like Metacritic where reviews have come in from many places and averaged. If you were to use this somewhat subjective but very factual approach, it is hard to consider games that are 97 (Halo), 95 (Halo 2), and 94 (Halo 3) on Metacritic are not AAA...

This would mean Killzone 2, Uncharted Drake's Fortune, and MGS4 would also fall out of AAA status... Now, although I am not the biggest Sony fanboy out there... I definately think those games qualify for AAA status...

In fact, really all you would have left is Grand Theft Auto IV if you use above 97 as the bar for AAA. I doubt anyone would agree that GTA IV is the only AAA game out there.