PlanetXbox360: "With Call of Duty: World at War's initiation into the Call of Duty franchise, comparisons and preferences have been widely expressed and slung around unnecessarily frequently. Back when Call of Duty 3 came out, the talk wasn't nearly as heavy, and the winner of the battle was clearly Call of Duty 2 over 3 (or at least in my niche of friends). But now, Treyarch managed to, and I have no idea how, totally confuse the hell out of players as to the simple question of "which game is better." It's hard to say, really, since the two are, at their roots, the same game, albeit visual aesthetics are greatly improved and, well... all the inherit stuff that comes from being in World War II again.
There are differences between the two, though, some significant and some not, so I've made list of them. Since World at War is merely the same game with several new features in a blatant attempt to one-up Infinity Ward's game, I'll be structuralizing this list to display the best features; contrarily, for Call of Duty 4's list, it will be comprised of features that couldn't translate over to World at War; from either design choices, or being 70 years in the future, they will be mentioned."