I beat it on it's hardest setting in ~4 hours one night and in one sitting, turned around and sold it to a friend for $40 less than 2 hours after that. This game was such a waste of money and a disapointment that I didn't even own it in my library for more than 24-hours. I like a game that can challenge me and that I won't want to be able to discard as completed and played-out in less than a dozen sittings in a month. Go try the demo like I did, but then don't buy the game, it's just not worth it compared to what else is available for choices right now (Modern Warfare 2 and Bioshock 2 I've been very happy with this year).
I'm not overlooking that the game does have some good strengths, but if it doesn't have the story/level-design to really utilize the goodies they gave us, what's the point then of this game? This game is good for only one thing IMO, as a one-night or weekend rental from your local video store.