Unfortunately there is no boggle-eyed, urinating David Shrigley giant at this year's Turner Prize exhibition. Glasgow would have loved that. But, no, that was two years ago and in another country (Northern Ireland). More's the pity. I could have done with some peeing in a bucket to lift the mood.

Ach, maybe I'm just having a bad week, but walking around the Tramway for this year's exhibition was an experience that registered somewhere between morose and miserable. There's not much to like on display. That in itself is not a problem. Who cares what I like? But the lack of something to challenge, to provoke, to engage, to admire, to pick an argument with is.

The watchwords for this year's Turner Prize shortlist have been "political" and "social engagement". There's been a suggestion too – from outgoing Tate Britain director Penelope Curtis no less – that the prize has become more "serious". (Does that suggest that in the past it wasn't?) And in defence of the artists whose work has been nominated, there are interesting ideas and artistic practices represented here. But good intentions don't make a good exhibition.

And this isn't a good exhibition. Some of that, of course, has to do with the nature of the prize. The nominees have been selected for work they have done before and elsewhere. And some of it is not easily reproducible in the gallery context.

Which is why this year's most intriguing nomination, the 18-strong Assemble Collective, seems particularly badly served here. Assemble have been busy in recent years reclaiming "tinned up" buildings in Liverpool to create affordable housing and creating "junk" playgrounds for children in Dalmarnock. Their work, then, is a form of architectural play which is also asserting both an alternative to the commercial imperatives of the housing market and a belief in "handemadeness" and craft.

In Tramway – which has been emphatically divided up for the Turner – they have built a house-shaped structure into which they have placed a showroom for Granby Workshop, a new social enterprise they have helped set up in Granby in Liverpool manufacturing products for the home. Here are mantelpieces and bookends and tables and planters and lamps and trivets and door handles and tiles. Assemble can say – ask them and they will say – that this is an extension of their social practice.

Fine, but what makes their work interesting is how it engages with the people in the communities they work in. In which case shouldn't they have created a workshop rather than a showroom here?

That's a missed opportunity. There are at least two works that are just misses. Full stop. Nicole Wermers's minimalist installation, the first you come to in the exhibition, is one of them. It consists of a number of vintage furs sewn onto the back of Bauhaus chairs designed by Marcel Breuer arranged in singles and groups of twos and threes.

Wermers has argued that they are a comment on ideas of private and public space, a response to a fleeting observation that people put their coats of chairs in public places as a statement of ownership. Is it though? Is occupation the same as ownership? Or could it be that people are just taking off their jackets to ensure they don't get their dinner on their cuffs?

And how are we to read the furs? Is this a piece about luxury or animal cruelty? About how we reduce living things to dead functionality? It's possible, I suppose. You can imagine these ideas swirling around the art, but they are just not animated by it, I'm afraid. The result is inanimate in every sense then.

Oh, and don't touch the furs. They're too fragile for that, I'm told when I enter. If only someone had thought that before they were taken off the backs of the luckless animals they once belonged to.

Bonnie Camplin's lo-fi room drawn from an exhibition entitled The Military Industrial Complex should be an X-Files fan's wet dream. Camplin says she wants to challenge "consensus reality". Why, she asks, shouldn't we take aliens and mind control seriously?

To investigate this she has gathered together novels, academic publications and the odd Wikipedia printout and placed them in a room with a few video monitors on which are playing her interviews with people who claim they are assassins in a worldwide feud between members of the Rothschild family or kidnapped as children and experimented on in a secret base in Banff National Park.

Sounds fun? It isn't. The presentation – think your local library circa 1976 – manages to render dull the most provocative of ideas. And while I was sitting in the room I kept thinking "didn't Susan Hiller do this before? And more imaginatively and visually too." Still, David Icke might love it.

At the entrance to Camplin's room there's a sign asking for silence. Wishful thinking given that the final Turner artist Janice Kerbel has been nominated for her work DOUG, a song cycle based on a series of catastrophic events (including being broken to bits by a bear like in the trailer for that new Leonardo DiCaprio movie. One line begins: "Out pops an eye …"). You can hear it everywhere in Tramway.

Kerbel spent years learning musical notation to make the work. It was worth the effort. The songs are clever and funny, the performances funnier and as the voices of the classically trained singers fill the Tramway space, they overwhelm the other exhibitions. Standing in Wermers's room as the songs filled the space, the fur coats on chairs get a borrowed oomph.

Kerbel's is by far the most entertaining and adroit exhibit here. Assemble should win the prize. But it's DOUG that you will come to see and hear. I'm not sure much else will detain you.