On this record, the band have cast a much wider net than previously, bringing together a broader array of influences than their earlier releases Leviathan and Remission, to create a record with far more depth than they have produced before. At the core of Blood Mountain is the grinding, guitar-driven metal, by turns melodic and dissonant, on which Mastodon have built their fearsome reputation. But Mastodon have taken this one step further, as Blood Mountain incorporates a host of progressive elements and fluid song structures which give the album another level of depth. Despite this reinvention, fans can rest assured: the same full-volume brutality of earlier Mastodon is here in spades.

What is it that makes Blood Mountain a compelling journey? For starters, we can look to the driving guitars and unrelenting pace of Mastodon's music. This is an exciting listen, although the album is crying out for even more variation and experimentation than the band have already imparted. Add to this plenty of quality riffage and a handful of unusual time signatures, and you have a record destined for success.

Vocals on Blood Mountain are split between singing and growls. Where clean vocals are used, they are very effective, with layered vocal harmonies bringing an extra dimension to tracks like "Siberian Divide". There isn't much lyrical variation here – material revolves around familiar themes, with an underlying mood of beasts, wolves and the forest at night (appropriate to the music at hand). It would have been nice to see some lyrical or vocal innovation here, but at the end of the day, the focus on this album is instrumental.

There are plenty of musical ideas on Blood Mountain, and very little filler, which keeps the album roaring along at full pace – a must for a band with such apparent energy. "Colony of Birchmen" builds from an enticing intro to deliver a full-blown metal symphony, Mastodon-style. "Sleeping Giant" is filled with enough hooks for a whole album by a lesser band. Album closer "Pendulous Skin" is another highlight, forgoing the customary heavy distortion and showcasing an introspective side to the band, more akin to Pink Floyd than earlier Mastodon, but still a welcome breath after the  crushing weight displayed in much of the rest of the album.

Mastodon's exploration of new ground on Blood Mountain breathes new life into their sound, but the album also highlights that this is a transformation in progress. Their song writing yields a great deal of frantic intensity, but in order to take their music to another level again, Mastodon must prove their versatility. The greatest problem with this album is an underlying similarity from track to track. Despite this failing, for an album built around the humble guitar riff, Blood Mountain does make involving listening.

To suggest that Mastodon are pioneers of experimental metal would be a mistake. What is clear from Blood Mountain, however, is that Mastodon have stepped up where many bands fail, looking to improve and revise their musical outlook rather than simply replicating their back catalogue. This album is not truly ground-breaking, but it does deliver on plenty of fronts. Blood Mountain showcases a group of musicians working at full strength, both individually and as a collective. This record is cohesive, heavy, full of quality riffs, and drives along at a pace to satisfy even the most impatient of listeners. There is a way to go yet, but Mastodon have sent an unequivocal message with Blood Mountain: the heavy heart of this beast is still beating.

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