SHORT. I got it on the PS3 and beat it in less than a week. Playing 1 - 2 hours a night. And I suck at this type of game. (Could never beat God of War 1 even on easy.)
That said, don't skip it just because it is short. (Though you may want to wait for a sale.) I bought it because Ninja Theory made Enslaved, a game I really enjoyed. Although I don't like this type of game much, the story was pretty cool (although some of the dialogue is very juvenile) and the environments were amazing.
Origin - JStarX7 STEAM - Agent.X7 PSN - JStar_X7 Xbox Live - Agent X7