Barozi on 21 September 2009
It depends on which difficulty you play it and if the campaign supports co-op or not.
ODST can be a 9 hours game if you play it on Heroic (the 2nd highest difficulty setting). I played Halo 3 with a friend on Legendary and we needed about 11-12 hours to finish it.
CoD4 on Veteran took me anywhere between 10-15 hours aswell.
Co-op can change the game experience dramatically so it's just like playing a new game.
