From what I can find it's about 12 hours long, IGN Australia says this and a couple other sources are around 12 hours as well. This is not looking through everything in the levels.

ive been playin games for many years and the first time i ever played knights of the old republic 2 it took me 27 hours to beat it........and for the force unleashed it only took me 3 hours and 31 mintes to beat i was really suprised at how easy both of those games were

The Path - Average 6h

Playing Titan Quest now, have played over 20 hours and I'm around half way. Will report once I finish it.

This List is what I've been looking for!!

WOW!
Great list and great job guys!

My contribuition:
Crisis Core: Final Fantasy VII - I finished my 1st playthrough in 15hrs
Final Fantasy X - I finished my 1st playthrough in 35hrs
Brutal Legend - 100% 12 hrs
Age of Zombies - 1h 30m (1st playthrough)
Demon's Souls - 55hrs

Lost Odyssey- 42 hours

Here are a few average times for some older games to fill some gaps in this great list.

Tomb Raider (original PS) - 22hrs
Half-life (original PC) - 18hrs
Call of Duty (1st PC game) 9hrs

Just Cause 2 - 20h. Could probably get away with 10h for completeing the story mode, but it would take at least 60h to get 100%

Titan Quest, 33 hours.

half life 2 was good, no doubt, but are you sure half life takes longer to complete than 2?