Over the course of five albums, Mastodon has perfected the art of melodic aggression. Like Metallica, the Atlanta metal band has translated gritty, surging, heavy rock tones into palatable songs that are easily consumed—and usually greedily so—by fans of all genres. On their sixth album, produced by Nick Raskulinecz, the musicians maintain what has worked for them on past efforts. If anything, there are a few smoother edges here: “Asleep in the Deep” eschews guttural riffs for silky melody and “Aunt Lisa” has an almost hooky rock quality in the chorus. But mostly, Once More ‘Round the Sun succeeds for the same reason that Mastodon always succeeds: because the balance between pummeling aggression and thoughtful, evocative songwriting is nearly perfect. Epic closer “Diamond in the Witch House” is the best expression of this, propelling the listener through eight minutes of visceral instrumentation reminiscent of 2009’s 13-minute “The Last Baron,” the undeniable opus that closed Crack The Skye.