Great thread! Why didn't I find it until now?!
Anyway, my personal times:
(I put a * in front of the games that I have pretty much similar hours to the main list to save your time Gilg, so u can skip those)
Assassin's Creed: ~18 hours
Assassin's Creed II: 31 hours (with both DLC. Without DLC ~27 hours) - What the heck with Assassin's Creed how people rush through them!
*Bioshock: ~15 hours
Dragon Age: Origins: 76 hours (with all DLC but not including Awakening. DLC took around 10 hours)
*Dead Space: 15 hours
Risen: 40 hours
Dark Messiah of Might and Magic: ~15 hours
Dante's Inferno: 13 hours
God of War 3: 17 hours
*Alan Wake: 11 hours
Red Dead Redemption: ~40 hours
Fallout 3: 65 hours
*COD Modern Warfare 2: 6 hours
*Uncharted: 12 hours
Wolfenstein: 11 hours
Demon's Souls: 68 hours
Mount & Blade: Warband: this is hard to measure because the damn game never seems to end but I've spent at least 80 hours and I've conquered about half the map.
*Oblivion: those 130 hours on the official list sounds reasonable (glad you guys took your time) although I personally spent at least 3-400 hours on my first playthrough but then I'm a fanatic about this game.