Way too hard
The walkthrough is practically useless, since the time you actually need the walkthrough is the so call "skill" level, in which it's only hoping that we cna even land a shot on the head, when they are staning.
you want skill? Then for those so-called skill level (I am talking about level 10, mainly) that there is an alternative, since there is no way I can get through that... shooting only while they are standing up, at their head? What the heck...
As for the others, yes, you will need patence, so those are good. In fact, had it been less on the "skill level", it would have been a ten.