Number 1. For some reason, the developers thought it would be a good idea to have several points where something just jumps out at you, out of the blue, and at a point where you had absolutely no way of knowing it was going to happen, or more importantly, could do nothing about it. For example, at one point I stepped out of a lift and this thing just jumped straight at me…there was no way of avoiding it. This would not be that annoying were it not for the fact that health packs are a scarce commodity and you waste some health fighting it off (see below)
Number 2. This relates to the above. Such unexpected attacks get followed by silly cutscene type incidents where you have to repeatedly press the A button like some demented typist to try and shake it off. During said cutscenes, you can't use any of your weapons and basically have to sit back and wait and hope you have bashed the button to a sufficient degree to shake it off. Again though, valuable health disappears.
Number 3. A problem with 3rd person shooters is the camera angle when fighting. Sometimes, you're left floundering mid fight, facing completely the wrong direction or jammed in some corner shooting at the wall. Frustrating.
Basically though it is a good game, well paced, superb graphics and a variety of missions. I also like the fact it is a slightly more refined FPS game which satisfies without the need for constant, blast 'em round every corner type action which so many lesser games fall into when they can't be arsed developing the storyline.