User blog comment:Carbonite 0/MW3 Real Life Achievements/@comment-75.158.175.91-20120215010740/@comment-92.84.46.217-20120216182614

It's around 5-6 hours on any difficulty anyways. The only things that hinder you when you can just run past everyone are those annoying scripted sequences and pitiful useless cutscenes, those might make it seem longer than it actually is. Gameplay wise it's very short.