The Gunman (starring Sean Penn, with Idris Elba & Javier Bardem) is a reasonably enjoyable action flick. The problem is that absolutely none of the movie is original. The movie is a variation of several action movie cliches: (1) Old Spy is ready to retire but his old life (or an old "job") catches up with him. (2) Old Spy faces the fallout of having to have left the love of his life because of a job. (3) Old Spy reforges old romantic relationship. (4) Old Spy does humanitarian work to appease old sins. (5) At least one old spy friend bites the bullet for helping out Old Spy. (6) At least one old spy friend turns out to be totally responsible for all the current crisis. (7) Old Spy travels to various locales involving at least one third world village & at least one really neat, old European city. There are other, less-over-used themes as well. For instance, The Gunman borrows memory loss from The Bourne Identity (to be fair, it is chronic neurological damage, not amnesia).
The best thing that one can say about The Gunman is that it is not awful. If you enjoy movies about gunplay, or movies about semi-retired spies kicking butt (Taken), then watching The Gunman is a perfectly acceptable way to spend a couple of hours.
The verdict: C ... Catch it on Netflix in a few months.