Appropriately—considering he built his early legend with scrappy, underground cassette releases—there’s an unpredictable mixtape quality to Beck Hansen’s first official album. Sonic trapdoors and restless experiments in style lurk everywhere (see campfire rock-meets-electronica twin-pack “Blackhole” and “Analog Odyssey”), as the L.A. native conjures inscrutable funny-dark tales of destitution (“Beercan,” “Soul Suckin’ Jerk”). Then there’s “Loser”: a skipping folk-rap masterpiece that—just like Mellow Gold—is as unclassifiable as it is giddily irresistible.