Mother Courage and Her Children, National Theatre

Bertolt Brecht was probably made for them: Deborah Warner directing Fiona Shaw in Mother Courage and her Children is as desirable a coupling, surely, as the Warner-Shaw Richard II or Happy Days, both immensely satisfying showcases for the director's imaginative reach and the actress's fabled versatility.

Warner has opted for a hybrid approach. The time is now, 1624 transposed to a shellshocked Iraq or Helmand: a critique of current US-UK foreign policy is loudly intended throughout. Yet each scene is flagged up in a black scrawl across giant unfurled sheets, a curious and some might say retrograde tilt at traditional Brechtianism: a device littering, with pesky plot-summary placards, early productions and far too many later ones. It looks antiquated and tiresome. But the Brecht Estate is known for its strictnness; maybe Tony Kushner's new, easy, expletive-ridden English version was bought at a finger-wagging price.

The Olivier stage is eviscerated at the sides and at the back, so we are treated too, most of the time, to the bits and bobs and gadgetry of stage management, including stage hands wandering around in headphones and, at one point, bopping.

Which brings me, briefly, to the music: I've not heard of Duke Special, though the programme note says songs from his first album have had "massive airplay on national radio" - my dial has clearly been in the wrong place. He has an enchanting voice and his compositions are sinuously melodious, rocking up a notch or two when the action requires it. But for a play that trades in bitterness, raucous barter and death, this score sounds preposterously twee: with his weird hair-do, moreover, Mr Special had me thinking of Rufus Wainwright in dreadlocks.

This isn't the right thing to be thinking of in Brecht. Here's worse news: Fiona Shaw sings. In fact, she erupts into the Olivier from below atop the essential Courage wagon looking like a Goth moll, and I wondered from the off whether Warner was, for perhaps rather base motives - the National has a famous record for noisy hits - aiming to twist Mother Courage into a musical.

If Shaw has a forgettable singing voice, her acting is thankfully full of verve, vituperation and passion: perhaps sometimes too much so. The staging as a whole can be criticised for too much attack and, frankly, amongst the smaller soldierboy parts, too much bloody shouting. However, this is mitigated by an engagingly modulated performance by Stephen Kennedy as the Chaplain, by turns scared and forthright, the Fool to Courage's Lear, and a fully studied, moving realisation of Courage's simpleton son Swiss Cheese by Harry Melling.

Shaw herself can of course be electrifying, as when asked whether she knows, by looking at his bloodied naked corpse, who the murdered Swiss Cheese is: recognition would bring about her own end. Shaw denies her dead son, nodding in agony, with that penetrating emotional detail she's justly renowned for. She's never less than watchable, always thinking or planning something, never still, never dull. But does that make her a defining Mother Courage?

It may be that she's unable to turn sharp focus on the part because of the sheer diffuseness of Warner's production: it has heart but not enough head. We're entertained by this Courage but left strangely unenlightened. And the coup de théâtre, at the premiere at any rate (I wonder whether this will or can be repeated every night), was the appearance at the end of the curtain call of Gore Vidal in a wheelchair: the US's most outspoken anti-war celebrity intellectual had read, live, the connecting scene-headings. Quite how his few choice words about remembering the Second World War and assertion that "war goes on" added to the drama was anyone's guess.

• Mother Courage and her Children is in rep at the Olivier Theatre until 8 December.
• Check out what's on at the National Theatre this season