A few corrections I'd like to make. Only Campaign, of course, as the rest is too variable.
God of War - Average: 9 hours
God of War II - Average: 11 hours
Shadow of the Colossus - Average: 12 hours (maybe I'm just slow lol)
Assassin's Creed - Average: 11 hours
Resistance 2 - 7 hours
God of War: Chains of Olympus - 7 hours
And some others:
Metal Gear Solid 4: With every cutscene: 25 hours, with no cutscenes, 15 hours.
BioShock: 12 hours (or so)
Tools of Destruction: 10 hours
Most games are around 10-12 hours, for me.
I beat MGS 4 in 14 hours watching all cutscenes. So actual gameplay is about 8-10 hours + cutscenes 4-6 hours.