For their seventh album, 2005's Robot Hive / Exodus, Clutch expanded their sound by adding a full-time organist to their lineup. While intelligent, unconventional hard guitar rock remained their main stock in trade, this change helped create one of the band's most diverse and satisfying albums.

Robot Hive starts off in a surprisingly unassuming manner, as singer Neil Fallon tells the tale of a couple on the run over the (relatively) unadorned guitar riff of "The Incomparable Mr. Flannery," humorously name-checking REO Speedwagon, Kansas, Boston, the Delaware Destroyers and Dokken along the way. It's not long before the song starts to reveal some typically Clutch twists and complications, and by the time the second track ("Burning Beard") kicks in, everything's already at a full boil.

The new keyboardist, Mick Schauer, makes his presence felt in varying degrees song-by-song. He trades licks with guitarist Tim Sult on "Never Be Moved," offers longer explorations on the mostly-instrumental "Small Upsetters" and, with bassist Dan Maines and drummer Jean Paul Gaster, creates a lush, warm bed for the verses of "Gullah." He shines especially bright on the numerically-titled "10001110101" (yes, that's actually the chorus), venturing far into Jon Lord / Deep Purple territory while Fallon fervently testifies about ribonucleic acid freakouts and the robot lords of Tokyo.

(Of course, the always-impressive work of Fallon, Sult and Gaster, and Maines remains the main focus here. But if you're telling the tale of Clutch album-by-album as we intend to do over time, what stands out about Robot Hive is how seamlessly and successfully they integrated this new element into their music.)

Schauer would stick with Clutch for one more record, 2007's From Beale Street to Oblivion, before the group reverted to their four-piece lineup for 2009's Strange Cousins from the West and 2013's particularly awesome Earth Rocker. The band is expected to release their 11th album, Psychic Warfare, later in 2015.

See the Top 100 Albums of the '90s

Criminally Underrated Albums

More From Ultimate Classic Rock