Although he often sang of the down side of life and referenced some of his own past -- he was in the audience when Johnny Cash played San Quentin, and not as a guard -- Haggard's songs almost always had an easy swinging feel to them. He managed to somehow use that mid-level sweet spot to temper his happy songs with a tinge of sadness and ease the blow when he sang about tragedy and loss.
Although usually looking a little dour when he sang, Haggard did have a sense of humor and could also do credible impressions of several of his fellow country artists. Here Glen Campbell coaxes a few from him, helped by a couple of friends:
Haggard kept performing almost until the very end of his days, even though modern country radio seemed to have little use for him except as a name-check a current singer would use in a song to try to establish twang bona fides. Most of those are silly. When Gretchen Wilson proclaims she's among the few women left who "eat fried chicken and dirty dance to Merle" you have to scratch your head. Because if there's a Merle Haggard song that can be used for "dirty dancing," I can't for the life of me figure out which one it's supposed to be.