My first experience of Amiina was seeing them support Sigur Rós in 2005. I think it was the first time I heard a musical saw played like a classical instrument, but my presiding memory is the audience talking over them. It was so minimal that people thought they were just tuning up or something. I have to admit I didn't find it too engrossing myself.

2007's Kurr was their first foray into album territory, a patchy record that most reviewers didn't quite know what to make of. A few years down the line and the former quartet is now a sextet, thanks to the addition of drummer Magnús Trygvason Eliassen and electronics man Kippi Kaninus. This expansion has allowed the band to develop rhythmically as well as sonically, offering more of a sense of progression and better distinguishing one track from the next.

But on Puzzle, many of these developments come at the sacrifice of the band's original character. The more upbeat tracks skirt dangerously close to sounding like the unreleased outtakes of their more successful contemporaries. 'Over and Again' is built on pizzicato strings, xylophone and theremin and could easily (but perhaps slightly cruelly) be described as 'Diet Múm'. In the same vein, 'What Are We Waiting For?' is cheery enough but doesn't really inspire past the point of niceness, a catchy vocal refrain keeping it afloat but not elevating it. The core of 'In The Sun' is formed by a chorus of mandolins and dense vocal harmonies, while the blend of male and female voices achieves an interesting texture.

When the singing is dropped the dynamic between old and new band members seems to tighten. 'Pusi' is laced with contrapuntal harp melodies, lending it a vaguely oriental tone belied by shimmering analogue synth pads. Increasingly complex and meticulous rhythms build before falling away to nothing. Open 'Asinn' takes a similar approach, swelling with nervous tension and embellished by drum patterns that lend a tribal urgency. 'Sicsak' may be the only one that really peaks like it should. Its cryptic instrumentation creeps along but is given a kick by a galloping, lopsided beat that is unexpected and strangely alluring.

Despite my initial gripes about Amiina's stubborn minimalism, it is the grittier tracks that fare best on Puzzle. The starker instrumental numbers are what this band does best, but sometimes they appear to be treading water by building tension just for the sake of it. Maybe I've listened to far too much post-rock to be an impartial judge, but a lack of release or catharsis means even the best tunes leave a faint aftertaste of frustration and unfulfilled potential. There has to be a sweet spot between minimalism and pop, but for now Amiina lurk between the two, seemingly unaware of the problematic nature of this contradiction. Incorporating oblique melodic sensibilities with their more recent penchant for accessible song structures will be the band's next challenge. True to its name, Puzzle feels like one of those gigantic jigsaws that is missing its most important pieces. Of course, you don't notice this until it's too late.