I see this poster and I immediately like it. It sums up what the movie is about. The character appears to be running away, (as opposed to chasing someone). He is facing (our) left and is moving to our left yet is placed poster-left, leaving the majority of empty space behind him where an unseen antagonist is giving chase.
If you look at what is behind the character all you see is out of focus highlights. This creates uncertainty and enhances the feeling one is being followed. It also lends more power to the antagonist. That is, the bad guy is frightening enough for the protagonist to run like hell despite the fact we can't see that anyone is giving chase.
The shot is done with a telephoto lens the way a sports photographer would cover an event, which creates an objective feel -- the viewer is watching from a distance (where it's safe), more of a disconnected observer, and is not an integral part of the action. This isolates the character from us making him appear more alone, more separated from anyone who might care or watch out for him. The telephoto lens also creates compression, which is the illusion that distant objects are the same distance as close ones. This ramps up the sense that the character is being chased because whatever is behind him appears closer than it really is -- a typical nightmare scenario.
The character's index finger is on the trigger of the pistol. A rather uncool thing considering the normal 'finger alongside the weapon, flat and off the trigger, very cool and benefiting from lots of training' look usually favored in the movies. This yields a gritty feel that conveys the gravity of the subject matter -- appropriate in the current environment. Of course, this may have been done simply to avoid having the character look as if he did not have an index finger on his right hand as it would not have been visible if it were flush against the far side of the weapon. Even if that was the case, the end result still works despite being a convenient side-effect.
Another effect that stands out is the use of vertical lines across the entire poster. These are the kind of lines you see if you look closely at a CRT video monitor.