In the same grain as "The American" and "The International", "THE (notice a trend?) Gunman" is a international thriller/action. Where the former 2 films focus more on the thrill, and are overall failures, Gunman is more action, and much more entertaining. If you are looking for a fairly low commitment to a 'smart' action movie, then you can do worse.
In 2006, Terrier (Penn) works for a global corporation (that might as well be called Umbrella Corporation) and is asked to kill a high ranking diplomat. The movie then skips ahead to the present where Terrier is not being chased down by unknown assailants. Nothing original there.
Terrier (Penn) is a likable character. Penn tends to be an actor your either hate or love, but he is does a good job as a grittier, more realistic Jason Borne. The movie ties to humanize him, but that side plot is mostly a thud. After Penn, the cast is stellar - however underutilized. It really is the peak of 'hey that guy' British actors. Unfortunately, Elba who gets second billing is in the movie for 2 scenes total and less than 3 minutes screen time, a role that has so little to it that I might as well have played the character. Winstone and Bardem exist, but their talent is mostly wasted.
The movie is a step sideways from a classic action movie. If you like the Borne series and its fast paced action you likely won't enjoy the more 'realistic' violence of "The Gunman". Unfortunately, if you are not interested in the Borne series, this likely won't be of any more interest. I give the movie a 7, because I enjoyed it. It is far from perfect, I feel the movie definitely 'left sometime on the table' in terms of directing and acting, it misses often in character development, and the movie kind of devolves into cliché, but there is enough substance to watch.