World at War without a doubt.. from the ridiculous grenade spam to the infinite respawns of enemies; it was by far the hardest of the CoD's for me.
MW3 is by far the easiest.. I finished everything in the campaign on Veteran in just under 9 hours.
100% RPG's: 49
Proudest: Star Ocean; Dark Souls; Neverwinter
Failing to Understand our Capacity for Kindness