Atlanta kings of sludgy prog metal, Mastodon, ventures into mainstream territory with a simpler, more hard rock approach on its sixth full-length release, Once More ’Round The Sun. On its 11 tracks, topsy-turvey grooves, memorable hooks and spaced out melodies are splendidly combined. There aren’t as many full-on guitar solos as in the past, but there are some tasty leads throughout the recording. Brent Hinds and Bill Kelliher play off each other so well that it’s like second nature to them by this point. Drummer Brann Dailor is always at his best, but here, he tastefully holds back on his furious fills more on this album than any other. They are still present, just a little more rhythmic. Troy Sanders’s lead vocals are so distinctive that they will forever be associated with the core of Mastodon’s overall sound. Some odd treats pop up here and there on Once More ’Round The Sun; Neurosis screecher Scott Kelly appears on the lurching "Diamond in the Witch House.” In fact, he’s appeared on every Mastodon album since Leviathan. There’s also a Faith No More moment on “Aunt Lisa,” complete with “cheerleading” vocal gang chants, courtesy of the all-girl punk band The Coat Hangers. The title track, with its inviting singalong chorus, contains a line from Thin Lizzy’s “Cowboy Song.” Each album in Mastodon’s existence has been equally innovative and unique in its own way, and Once More ’Round The Sun is no exception.