Garage Inc.

Metallica are deep into midlife crisis. The band’s last two albums, “Load” and “Re-Load,” were transitional affairs that found our boys continuing to move away from their characteristic speed-metal symphonies toward a sound not unlike — yikes! — alt-rock. Now the two-CD “Garage Inc.” finds Metallica executing the ultimate water-treading maneuver of a band in flux: a covers album, with one disc consisting of 11 “new” oldies and the second gathering all of the band’s previously released covers.

There’s nothing inherently ignoble in a band taking a breather and bashing out a bunch of songs they love for sheer fun; often — as with Guns N’ Roses’ 1994 “The Spaghetti Incident?” — the resulting album can be pretty swell, and certainly preferable to a cobbled-together collection of subpar originals. And in the case of Garage Inc.’s “new” songs, the choice of material is so esoteric that most metalheads will be lucky if they recognize more than two or three of these tunes, much less some of the bands who originally laid them down. Discharge? Diamond Head? The Anti-Nowhere League? In a few months, they can all thank Metallica for reminding them what a royalty check looks like.

Far more surprising than Metallica’s well-documented taste in obscure punk and metal is their newfound embrace of classic rock. The crunchy retooling of Bob Seger’s burnout ballad “Turn the Page” is a standout, and the soulful acoustic jam on Lynyrd Skynyrd’s “Tuesday’s Gone” makes the 12-minute Mercyful Fate medley sound like the rote wank-fest it is. Forgotten album tracks by Blue Oyster Cult (“Astronomy”) and Black Sabbath (“Sabbra Cadabra”) also pack a wallop — as do a wholly unexpected take on Goth king Nick Cave’s “Loverman” and a gallop through Thin Lizzy’s “Whiskey in the Jar.” We’ll have to wait until Metallica’s next “proper” album to find out if this trip to the garage recharges their batteries. Still, all things considered, “Garage Inc.” is an intermittently exhilarating joyride.