It's always a delight to enter Aix's bijou Théâtre du Jeu de Paume, newly restored for the millennium and the scene of some notable successes soon thereafter (William Christie with Il ritorno d'Ulisse in patria; Daniel Harding with The Turn of the Screw). Lately, though, it's become the venue for events at the more recherché end of the Aix Festival spectrum.

Here's one such. Svabda (Marriage), by the Serbian composer Ana Sokolović, can scarcely be described as an opera at all beyond the fact that six women sing onstage for 50 minutes. That's fine, of course; some works defy categorisation. The problem with Svadba is deciding what it was that directors Ted Huffman and Zack Winokur sought to achieve by applying a dramatised context to this semi-abstract soundscape.

A young woman readies herself for marriage while five friends help her with the preparations. There's gentle banter, a few tears and a substantial amount of wordless vocalising among the fragments of Serb until her big day arrives and the girlish bride sets forth, strengthened by a new-found maturity. It's sung a cappella apart from some charming interventions on the ocarina and a few moments of improvised percussion, all played by the singers themselves.

Sokolović's piece falls into two distinct moods: the first episodic and playful,  dominated by Kodály-like rhythms and rather too much unfocused jollity; the second hauntingly beautiful as Milica, the bride, sings a wistful song of farewell to her friends as they dress her and send her on her way with the dubiously encouraging enjoinder "Don't look back... ". This extended finale, embellished as it is by touching chromatic harmonies, helps banish the mild irritation that's built up over the previous 35 minutes of binless Stomp and freewheeling Serbian scat. If the chuckles were a challenge, the Clanger-like noises were a trial. I remember glancing at my watch after half an hour and ten minutes had gone by.

No blame for Svadba's weakness rests with the performers, all of whom – not least the discreet but decisive music director Dáirine Ní Mheadhra – deliver the material with great conviction and talent. The soloists are all terrific, especially the Canadian soprano Florie Valiquette as Milica, but Huffman and Winokur have them splash about on Samal Blak's all-but-bare stage like a meet-and-greet impro at a drama workshop. It's especially puzzling since Huffman has done exciting work elsewhere, not least in English Touring Opera's pitch-perfect staging of Maxwell Davies's The Lighthouse. Here he leaves us beached with six singers in search of an opera.