To paraphrase a line from the movie, the Coen brothers’ latest is like a great folk song: It’s familiar but feels new. Set in the 1960s, this serio-comic portrait of a self-sabotaging, second-tier folk singer, Llewyn Davis, represents one of the sibling filmmakers’ small, piquant canvases, more on the scale of A Serious Man than True Grit or No Country for Old Men. Although loosely inspired by Dave Van Ronk’s sunny posthumous memoir, this is an undistilled Coen brothers concoction of surreal dread, misanthropy, hostile encounters and precision-timed jokes. Llewyn (excellently played, and soulfully sung, by Oscar Isaac) has the abrasive ego of a young Bob Dylan, without the genius or success. He travels Manhattan in search of couches to sleep on between infrequent gigs. As his former lover, Jean (Carey Mulligan), now the wife of nice-guy folkie Jim (Justin Timberlake), repeatedly reminds him, he’s “a loser.” In tone, the film hovers between Barton Fink, with its grim portrait of the ugly side of the entertainment biz, and the comic O Brother, Where Art Thou?, as an episodic journey of weird encounters, accompanied by a savvy period soundtrack, overseen by T-Bone Burnett.