As is common in these kinds of threads, most people with 360 tags will say Alan Wake and most people with PS3 tags will say Killzone 2.
I'll say; I don't quite know but it seems likely to be Killzone 2 if only for the fact that its already well beyond 2 million and is still moving somewhat and Alan Wake with its genre mixing and hit or miss gameplay (don't get me wrong, I think the gameplay looks superb but its appeal might not be broad, same as with Heavy Rain) is a shot in the dark.
Speaking of dark; Alone in the Dark, which is probably among the closest cousins to Alan Wake has sold poorly, another indication that it might not be a smash hit.
Will it still be a part of my collection? God yes.
Luckily for me, my enjoyment of a game comes not from the sales but from the quality of it (in my strange ways I've found that I like both DiRT and Valkyria Chronicles despite low sales).
PS: I would be interested in hearing some good arguments as to why Alan Wake would sell more though, just for the hell of it.







