1. Headshots are non existent. It doesn't matter if you hit human enemies head twice or even three times, they will still be on foot shooting at you like if your bullets were made of plastic.
2. Lack of substance. Even though the game have some innovative stuff, the story is terrible. On time it becomes boring. Characters could be more developed, they lines and evolution feels really shallow through the game. Especially if you've played other story driven shooters. This flaws make this game only a shallow shooter with great graphics.
I think this game is overrated for what it offers. Graphics are not everything. And a shooter with NO HEADSHOTS it's a terrible experience for any serious FPS gamer out there with some decent skills and taste for the genre. The AI is pretty decent, but far from being innovative. It resembles the first F E A R AI, with some improvements. This game is ok for a single playthough, but it terribly fails to grow on you.