It's about time someone wrote an opera about the internet. And who better than Nico Muhly - snarky blogger, snappy Tweeter, and according to the Daily Telegraph "the hottest young composer around"? Add seasoned playwright Craig Lucas, top Broadway director Bartlett Sher and some of Britain's finest singers, and you might expect them to cook up a success. The ingredients do sound promising, but the souffle fails to rise.

It's not spectacularly bad. Perhaps in recognition of the production's future transfer to the very conservative Metropolitan Opera in New York, both music and staging are tame (though anyone easily shocked should be warned of a couple of graphic on-stage masturbation scenes). In the end, it is perhaps this lack of adventure which is its downfall.

Muhly's premise is certainly fascinating. A 16 year old boy stabs a 13 year old he met in an internet chatroom. It turns out he's been tricked into attempted murder by the younger boy himself, who assumed various online disguises - a girl, a spy, a homicidal gardener - to spin his story.

The tale is told in flashback, as a hard-bitten and improbably internet-inept policewoman (shades of Prime Suspect) slowly puts together its pieces. The attentive audience member will probably solve the puzzle in minutes though.

Dramatic tension is fatally lacking. Whether traditional or modern, opera thrives on grand gestures and overwhelming emotions. Two Boys is short of both. The action unfolds slowly and predictably. Even the stabbing itself oddly lacks impact. Neatly orchestrated, Muhly's music mostly just burbles along contentedly beneath like a polite movie soundtrack (a genre in which his efforts, including The Reader, have been widely praised).

There's little of the unfriendly dissonance that contemporary opera is notorious for. The repeated figurations recall Michael Nyman, and the choral chatrooms carry a whiff of Eric Whitacre. A stretch of chugging syncopation is almost an homage to John Adams, and a little gamelan-style percussion nods in Britten's direction. It's as if the music has as many identities as the opera's protagonist. Now and again they add up to a distinctive voice, but these moments are all too few. As it's a new piece, how much Rumon Gamba's conducting is to blame is hard to say, but the orchestra seemed to play efficiently.

Vocal lines closely follow the natural speech of Craig Lucas's libretto, melodic but hardly memorable. For once, the surtitles do more than just compensate for poor diction as they display netspeak like ASL and BFN while the singers mouth the full words.

Susan Bickley carries the show as DI Strawson, with Valerie Reid entertaining as her elderly mum, forever nagging her to find a man. Chunky twenty-something tenor Nicky Spence barely passes for the duped 16 year old Brian. There's a faintly creepy man-boy frisson between him and Jonathan McGovern, who must be close in age to the 13 year old, Jake, he plays. Heather Shipp, Mary Bevan and Robert Gleadow impress as Jake's alter egos.

The music is framed in a production as untroubling as the score. A single drab set serves for all, with basic furniture moved on and off to vary the scene. Projections by 59 Productions create a more enticing virtual world of flickering lights and flashing texts. But it was a long two hours all the same.