In their six-year existence, Mastodon have swiftly become "exhibit A" in the case for the defence against the oft-heard accusation that heavy metal is nothing more than cock-rock misogyny and shock-and-awe teen fodder. Not only did they write a concept album based on Herman Melville's Moby-Dick, the US four-piece made the most enormous, bombastic music you could possibly hear, short of travelling back in time and taking up residence inside Wagner's brain. But within seconds of the opening track of this, their third LP, it's clear a significant change has taken place: syrupy, multi-tracked vocals akin to Supertramp in a particularly foul mood have replaced the primal roar of old, while their tectonic hugeness has been supplanted by the wearisome over-indulgence of musos at play. With an eye on the prize, Mastodon have sold their birthright for a mess of potage - or, in the case of the "song" Bladecatcher, presumably a homage to Melt Banana and Lightning Bolt - just a plain mess.