I played it yesterday. All in one sitting, just on normal difficulty. I absolutely loved it. The story left me speechless, it had tons of very intense and emotional parts. Even on normal difficulty, there were some parts where I had almost no ammo, no life and about 5-6 opponents to kill. I had to be very tactical about situations. They game makes you play smart, if you don't, it'll "punish you" and make things harder for you.
Definitely game of the year in my opinion.