Absolutely no chance to beat Halo 3 lifetime (as games become ever more frontloaded 1st week sales are a different thing. I don't care.). Anybody who thinks this can outsell Halo 3 is fooling himself.
First we have the generation effect. It comes very late in a generation.
Then we have the competition (which I think is the reason for the slight downward trend of Halo games). Call of Duty will steal more sales from Halo 4 than what it did from Halo 3.
And thirdly, while the game looks graphically very nice (but so does the competition) I see no other reasons for it to be perceived as better than Halo 3. It's impossible to beat that 94% Meta of Halo 3 (for comparison Reach got 91%).
9 million lifetime.







