It's a horrible term, to say nothing of a rancid commercial brand, but if any music genuinely qualifies as a 'guilty pleasure' then it's the Mars Volta. Overblown way past the point of pastiche, simultaneously future-radical and retro-conservative, ultra-po-faced yet ridiculous, Guitar World flashy and muso-sickening…their saving grace has always been that they know all of this but really don't give a shit what you think of them. They have an ability to barge through all preconceived notions of taste and acceptability by virtue of sheer kinetic energy and a maddening splurge of ideas.

Frances the Mute aside (which oozes awesomeness from start to finish, and I will disparage the reproductive organs of anyone who says otherwise), their albums usually get by on a certain craftiness of paw. Their highs are so preposterously lofty and brilliant that a scattering of utterly incredible moments can cast an illusion of brilliance over a whole record. Who can begrudge an occasional bit of turgid drear when it's just a respite between peaks of divine, giddily frenetic Latin psychedelic speed-prog?

So Octahedron is baffling. And a little sad. This is The Mars Volta denuded. Certainly still overblown, but now in a way that's largely slow, melancholy, restrained to the point of coma. Boxed into traditional song forms and radio-ready structures. They're as bloated as ever, but have for the most part cast aside the detonations and tangents that give their songs paradoxical charm. So what's left when you remove the giddy excess from a band like this?

Alas, not much.

The album trudges into life with 'Since You've Been Gone' - not a cover of Rainbow's finest hour, but a seven-minute melancholy ballad that could almost have been written for LeAnn Rimes. The slick arena funk-rock of 'Teflon' barely ups the pace or the adrenalin levels, but at least gets a little groove on. 'Halo of Nembutals' attempts to get psychedelic, but is half-arsed, recreating only the imperceptible buzz of eating immature chilies. It's 24 long minutes before Octahedron offers anything captivating, as the 'Immigrant Song'-esque riff to 'Cotopaxi' bursts in the door and trashes all the tasteful ecru furniture. Yet the song is over in under four minutes. In Volta-land, that's cursory, insulting.

'Desperate Graves' raises the energy levels to almost acceptable, before the insufferably maudlin 'Copernicus' sucks all the life out of the room and dribbles it down its chin. It falls to closer 'Luciforms' to save the day. All tangled, keening interplay, portentously echo-soaked vocals and high-ampage leads, it looks like it might just pull it off - but all hope is dashed when it stops at exactly the point where old Volta would have just been getting warmed up.

Maybe this is overly harsh, a failure to sympathise with the desire to make a more grounded and focused statement. By any standards, Bedlam in Goliath was a pretty full-on record, one whose energy it'd be impossible to surpass without suffering some kind of aneurysm. And if you've purposefully removed your frontiers, where is there left to travel except inwards? There's nothing wrong per se with tasteful maturity - it's just that TMV seem unsure what to do with it. The predominant AOR balladry is only slightly tinged with proggy weirdness - just enough to soften its potential communal impact, nowhere near enough to make it uniquely fascinating in its own right. Any one of these tracks may have been an incongruously beautiful respite in the midst of a more hyperactive collection, but en masse the cumulative effect is dispiriting.