No knock on Sean Penn for aping Liam Neeson and going all Action Jackson on us. At 54, Penn looks ripped and ready. As a producer, he hired Taken director Pierre Morel, found great actors (Javier Bardem, Idris Elba), co-wrote the script about Jim Terrier, an ex-mercenary atoning for past sins in the Congo, and — oh, why go on? The Gunman degenerates into dreary setups for guns and gore. Penn merits more. So do we.