I certainly do think the length makes a difference, why else would tons of people complain about lack of gameplay length. If a game is good, but way to short, it cleary affects the general experience. Imagine WW took 4 hours to beat, would you say its just as good?
And BTW, im sure the game is long, very long, like GTA long. Beating Vice City to the fullest could take 100 hours, perhaps something similar for this game, after all, LA is being rebuild in that game.