Here’s another group who have spent years on the road, perfecting their live act and building up popularity through word of mouth, hard work and bloody-minded persistence. And in Future Islands‘ case it certainly seems to be paying off, although their now legendary appearance on the David Letterman show can’t have done their prospects any harm either. The Flex was rammed to capacity on this occasion, and it doesn’t take a genius to predict that Future Islands will be playing much larger venues than this from now on.

So yes, I went along to this show out of curiosity and because, like everyone else it seems, I was intrigued by vocalist Samuel T Herring’s performance on Letterman. In a world of formulaic indie artists, here is someone with a unique and riveting approach to performance. Herring sings with undeniable passion and soul, but that’s only the beginning of what makes him a star. He dances in an extraordinary, utterly unself-conscious style, bobbing and weaving as if vast, unmediated emotions are coursing through his veins. When he’s not reaching out to the audience as if trying to connect with each and every one of them, he’s either growling like a dog or hammering on his chest like a penitent. It’s a wonderful sight to behold, and if anyone reading this hasn’t yet seen that Letterman clip, I urge you to seek it out on YouTube; it’s truly spectacular.

The problem, for me at least, is that the songs themselves are not strong enough to sustain interest for an entire performance. In Herring, Future Islands have one of the most charismatic frontmen I’ve seen, yet all the charisma in the world can’t hide the fact that the group’s songwriting ranges from the rudimentary to the insipid. The gorgeous “Seasons (Waiting on You)”, by a country mile their best song, is tender, melancholy and suffused with an indefinable longing; try as they might, however, the group are fatally unable to reproduce its magic elsewhere. Song after song proceeds on the basis of lazy, half-baked melodies oozing out of watery synth tones. Lyrically tendentious and rhythmically uninspired, this stuff takes its place at the end of a long line of unremarkable synth pop creations.

Now on the verge of a major breakthrough, Future Islands find themselves on the horns of a considerable dilemma. Without Herring’s lovable-dork persona, they would be just another bunch of chancers dolefully prodding at a keyboard. For now, they are able to bask in the considerable goodwill generated by their frontman’s undoubted appeal. Yet the thinner the act wears, the more Future Islands risk being rumbled as musical also-rans.