Sorry, but this needs work.
The main problem I have with it is that requires you to not just click quickly, but also rather precisely - and for no good reason, since this isn't a skill game. For instance, I have been literally unable to kill the guard that throws the grenade at you after you get out of the water tunnel; my character's taking off the dive suit, and when I can finally actually CLICK on the guard to kill him, I get a "how do you want to kill him?" menu. And since none of the options is either under my mouse cursor already nor large enough to hit with a quick flick-your-wrist-and-click, he always kills me.
IMO, that's a textbook example of fake difficulty. The game isn't bad otherwise, but this really ruins it for me. Sorry.