It was short on normal, only about 8 hours. I'd say that's standard fare for a shooter anymore though, and games in general. Doesn't seem like a lot of games are all about lengthy campaigns anymore. The only games that I've put more than 12 hours or so in to over the last year is Fallout 3 and Super Mario Galaxy.
Beat it on hardcore in two days (4 hour intervals) I have no clue how you guys stay on 10 hours straight! LMAO!!!. Tried insane, but way to hard! haha.. Will try INSANE on CO-OP though.