THE National Theatre in London is currently of the opinion that George Bernard Shaw "may be our most provocative contemporary playwright". This, one assumes, is calculated more as a compliment to the Irish dramatist (who died almost six decades ago) than an affront to our current crop of playwrights. Shaw, ever an ironist, would have been tickled to think that his brand of satirical, left-wing theatre would be so lauded by the National Theatre of the UK in the early 21st century.

Major Barbara continues to pack a considerable political punch. As the eponymous Salvation Army officer becomes reacquainted with her absent father (Andrew Undershaft, a millionaire weapons manufacturer), Shaw embarks on a characteristically Fabian morality tale. The drama revolves less around its title character (who has given up her life of luxury for a Sally Army shelter in the slums of West Ham) than it does around Undershaft. It is his words and deeds that determine his daughter's future course; indeed, as he makes plain (like a capitalist on a truth drug), he determines the futures of many millions of people.

The play positively bristles with wonderful, satirical one-liners; Undershaft's comment that alcohol "enables parliament to do things at 11 at night that no sane person would do at 11 in the morning" is a particular gem. However, the drama is also abundant with Shaw's twin weaknesses for polemical posturing and verbosity. These come to so dominate the third act that the play all but runs into the sand. The moral dilemma (regarding future ownership of the munitions business) should grip us to the end, but the tension melts away in the midst of speechifying.

If the play ultimately disappoints, director Nicholas Hytner's production does not. Tom Pye's design is superb and the cast is uniformly excellent, with Hayley Atwell playing Barbara with the fabulous breeziness of a self-confident heiress. The unarguable star of the show, however, is Simon Russell Beale. His unabashed Undershaft lives in his depravity as if it were an easy chair and makes the late Alan Clark MP (that other sayer of the unsayable) seem like an impostor.

If Major Barbara is too long by 30 minutes, The Wall - the latest offering from young playwright DC Jackson - is at least an hour longer than it should be. Directed by Gregory Thompson, with script development by Liz Lochhead, this comedy of small town adolescents feels like a short sketch stretched well beyond breaking point.

Jackson's story of the troubled nascent love between Stewarton teenagers Barry and Michelle seems unfinished. The key elements in the plot, from the lesbianism of Michelle's mother to the secret of Barry's father's unemployment, are introduced with a heavy-handedness that renders the play predictable.

There is a similar lack of subtlety in the characterisations and, most damagingly, the dialogue. From the awkwardness of young love (albeit laced with alcohol and vomit) to the drearily obvious spoonerisms committed by Barry's sister Norma, Jackson is too easily tempted by cliché. Even the character of Rab (the self-professed "bam", with a twist) struggles to get beyond Still Game ned caricatures (despite Finn den Hertog giving the best of four fine performances).