Rating: NN

Mastodon’s sixth is probably going to polarize fans the way their last album, The Hunter, did (and Crack The Skye to a lesser degree). It continues in the direction of that 2011 effort, with completely clean vocals and dense guitar riffage layered into thick sludge, but with even fewer hooks and thrilling riffs. The music still branches off into proggy places, especially in the latter half, but nothing hits hard or is remotely memorable.

Troy Sanders and Co. deliver some strong vocal melodies, and their accessibility and the album’s polished production values bring to mind Metallica’s Black-era evolution. Speaking of, it’s tough for any aging heavy band to find a sustainable musical direction – especially when your early albums were aggressive, seething, electrifying monsters – without losing vitality and a sense of adventure.

The titans of metal are making a valiant effort – Aunt Lisa surprises with female vocalists chanting “Hey ho, let’s get up and rock and roll” – but it’s not enough to prevent Once More ‘Round The Sun from being a slog to get through.

Top track: Aunt Lisa