Ever since they first appeared in the late 1990s, Iceland’s Sigur Rós have occupied a fertile middle ground between post-rock and classical. However, in contrast to the harsh, at times industrial soundscapes of 2013’s Kveikur, their first album in a decade (and first since multi-instrumentalist Kjartan Sveinsson returned to the fold) largely eschews percussion. Instead, the 10 tracks here, with strings from London Contemporary Orchestra very much foregrounded, tend towards slowly unfurling ambient washes of sound. Listened to as individual songs, the effect is undeniably beautiful, notably the way Skel builds to its climax before gently subsiding, and Jónsi’s vocals are especially affecting on the more subdued Ylur. Overall, though, there’s a disappointing homogeneity, and the start of the album in particular feels so overegged as to be almost cloying. It turns out there’s a limit to how much amorphous euphoria it’s possible to take in one sitting. Perhaps part of the problem is the fact that much of it sounds like devotional music, with Jónsi’s language-less vocals obscuring whom or what is being worshipped. Either way, Átta feels surprisingly unengaging.