It's not every day you see a martial arts movie which may be as violent as any horror flick released the same year. "Headshot" is one such movie. It might be second only to "The Story of Ricky" in terms of violence, but whereas that one was a cartoonish gore flick, this one is disturbingly realistic, at least in its handling of injury. Off the top of my head we have people getting stabbed through the head sideways, a loose bullet being jammed into someone's eyeball, and someone being impaled on a broken tree branch and then trying to pull someone else onto the spike. Also, countless people are shot to death. You've heard of the Hongkongese genre "heroic bloodshed"? You don't have to be a hero to shed blood in this one.
The "story" is the usual "violent man with no past saves people while other people come to get them". I think they tacked on some kind of non-explanation for how the violent characters got that way; something about a covert operation training child soldiers. From what you see of this shady business, it is impossible to believe that anyone could come from it and be proficient at fighting; it's one of the dumbest contrivances I have seen in a recent movie. These scenes don't depict a hardcore training program for brats: they're more like an extremely inefficient method to kill children en masse.
But you don't (and won't) care about that stuff. You care about the fight scenes, and yes, they are impressive. I didn't think they were as impressive as "The Raid 2"'s, but it's hard to imagine too many fans of those kinds of movies will leave this one disappointed.