Once the reviews start to pop up tomorrow onwards I think it will slip to 1# in no time. Many people that haven't pulled the trigger on buying the game will.
I speculate this game getting as low as a 9, but I know there's gonna be nitpickers out there that will complain and probably go lower than that, but Witcher 2 has 88~ meta score and from the footage we have seen W3 is leaps and bounds better AND open world...I don't think it will score lower, since every aspect of Witcher 2 has been improved on.
My speculation is purely based on 5+ hours of gameplay footage & streams that I have watched thus far.
People (at least on the console side) have been looking for a "Skyrim replacer" since 2011 and I think they will get it now. And to play something else than the yearly CoD & AC, because let's face it..the exclusive games (except Bloodborne) have been lacking greatly on both current gen consoles.