DCOK on 29 December 2012
In all honesty, it needs to be long, which helps with the replay of the game.
I voted 21+ hours, as it's very easy for developers to take a story with missions/chapters/sequences and draw it out for the player's enjoyment.
Although, that's not to say that short games lack in any way. God of War 3 was 7 hours, if I'm not mistaken, but was pure chaos and carnage for every second of those 7 hours.
