To be honest, I'm quite happy that the game is 50GB. I know that sounds crazy, but it looks like Infinity Ward are finally able to push things again, give their game engine a proper update. This engine might be intended to last the entire upcoming generation, after all, and PC development has long been hamstrung (in some terms) by the limitations of consoles. Why not push everything to the limit now that they can? It'd be good to see PCs suddenly leap forward again and actually reach somewhere near their potential.
Incidentally, the largest shooter download I can remember was Max Payne 3, which clocked in at 30GB on my Steam account.
Whoops, sorry, that was far too rational. According to thread narrative I should be screaming in frothing indignant rage that anyone might enjoy a shooter series enough to not give a damn about utilising the cheapest primary component of any system.