Metacritic != real living people (reviewers exist in a separate realm).
Er, metacritic reflects the average review score.
Anyway, you're still ignoring the significant price gap between GH3 and RB and how that obviously makes your comparison rather worthless. Price more than anything will scare consumers.
What about the bundle-less game? It is a pity we don't really get any differentiation there, but I think it's pretty safe to believe that GH is still the bigger franchise, notwithstanding the inferior game.
Also, Call of Duty was already a huge seller. Each game sold in the millions.
I don't know if you can use plural, though, and it's not even in the same league. CoD4 was over 10 million. The games always were big, but CoD4 wasn't just big, it was enormous. Those are Madden/GTA/GH numbers.
CoD4 was just a massive game, and I have serious doubts anyway game in the series, Infinity Ward or Treyarch, will ever match it again. It was a perfect release point, and really pushed multiplayer more than anything. CoD has been on a regular release cycle for awhile and even had poor old-console spin off games for it. Reviews will mention it's Treyarch developing this one, will note the even more lackluster single player, and copy cat multiplayer. The online community will likely not shift and this one will perform like your typical CoD game sales wise. Really good, not amazingly great.
You keep saying that reviewers will influence public opinion when I don't think they do. Word of mouth and brand appeal are far stronger; the review-reading people are mostly enthusiasts. These enthusiasts are important to spread word of mouth on a game, but they don't have that much influence beyond that. Do recall Assassin's Creed, a game with no MP component and mixed reviews, a mere 80 on metacritic, sold 6 million copies. That's 3x Bioshock, another game with no MP component but universally high review scores -- and with that big a gap, even multiplatform release doesn't explain it, before you go there.
CoD:WW has built up its own momentum. The MP beta may be enough to dissuade people from buying the game, but as I see it the game, unlike CoD4, will have a enormous first-day sales but will soon drop off, if the game really isn't that great. Unlike CoD4, word-of-mouth won't carry it further, but it'll still be big success. And yeah, maybe people will stick to 4 in MP, but if millions of copies have been sold already, it's not like Activision is going to be dissuaded from alternating good and bad developer houses for the franchise. It won't be as big as CoD4, it won't sell 10 million copies, but I do think it'll be one of the biggest games this year, mostly on brand recognition. The only thing that can really hurt CoD's image is the WW2 part; I don't think it'll resonate as strongly as modern weapons would.