As others have said, the controls, both on keyboard and controller, or horrendously setup. Your character never does what you expect him to because of pointlessly inverted controls and weird decision to quick tap two buttons to do a high jump. I don't understand how so much time can go into audio and visuals and so little on simple controller setup (which cannot be changed in settings).
Not much I can say about this game that hasn't already been said. It's a game that everyone needs to experience. I took just shy of 130 hours to do a playthrough of the main game and expansions. I don't consider myself an achievement hunter, but I literally finished every mission available (and there are a lot). It's the pinnacle of gaming, and I think it will be a long time before it gets dethroned.
