Marguerite, Theatre Royal Haymarket, London<br/>The Long Road, Soho Theatre, London<br/>The Pitman Painters, Cottesloe, London

Oh la la! This is, clearly, the height of passion: French kissing as your French windows explode. I knew that the new musical Marguerite – co-written by Alain Boublil and Claude-Michel Schönberg of Les Misérables – was based on the legendary Parisian courtesan Marie Duplessis. However, I never realised that being a sex bomb literally entailed detonation.

Hang on, no, my mistake. Staged by Jonathan Kent, this is an update of the tragic 1840s romance by Dumas fils. It's set a century later, in Nazi-occupied Paris. Here the heroine is an ex-cabaret diva and Gestapo commandant's mistress who falls for a boho pianist. So, Ruthie Henshall's Marguerite and Julian Ovenden's young Armand are, in fact, launching into their first dangerous liaison in the middle of an air raid.

If you ask me, this is laughably de trop as our heroine's palatial double doors are blown away and our smitten hero sweeps her off her feet – locking her in an embrace on the lid of her baby grand. There are points in Marguerite when – even if she is elegant in Chanel-style haute couture and he looks like the James Dean of Montmartre in his leather jacket – we're still basically stuck in a 19th-century melodrama. Ovenden is required to overdo it, especially when Armand believes he's been callously ditched. He tosses a blizzard of billets-doux in the air as the string section, in the pit, lets rip with the predictable crescendo.

Nonetheless, this is certainly a cut above your average West End musical. It may well prove to be a classy-looking crowd-pleaser, ending Kent's Haymarket season on a relatively strong note. To his credit, Ovenden is a talented enough actor to get away with OTT quivering ardour and Henshall can really sing as well, her voice on mellifluous form.

Scored by Michel Legrand, many of the songs have gently haunting tunes, with a touch of mournful ballad about them. The trio "Intoxication" – bringing in Alexander Hanson as the infatuated commandant – is an eerie kind of musical round where it sounds as if they are all caught in a shimmering whirlpool. Such moments go a long way to compensate for the banalities of the lyrics and the book by Boublil, Schönberg and Kent.

As for placing the love story within a bigger political conflict, that's excellent in theory and, for sure, the storyline is critical of the self-absorbed lovers whose thoughtlessness endangers Armand's Jewish friend and members of the Resistance. Nevertheless, by keeping the amour fou at the emotional centre while introducing citizens who are more valiantly engaged as mere secondary characters, Marguerite actually makes itself look shallow.

Shelagh Stephenson's new chamber play is far more poignant. It could have been merely worthy: co-produced by Synergy, a company that works with prisoners, and by the Forgiveness Project, a charity promoting reconciliation processes. But The Long Road focuses on a middle-class family devastated by the loss of a child. Stephenson has an acute understanding of the psychological contortions involved in bereavement, and Esther Baker's cast of actors – including Denise Black – is quietly superb.

Mary and John's teenage son has been fatally stabbed in a random attack by a hard-bitten, drug-addled teenage girl. Emma is now in prison, but her existence begins to obsess Black's Mary. It's almost as if the incomprehensible criminal is hogging the gap her victim's death has left. The mother has savage revenge fantasies but eventually feels she needs to understand and starts writing letters to Emma. This appals Michael Elwyn's John, who is aggressively determined to blot Emma out, slugging whiskies.

Crucially, what makes The Long Road searing is its intimacy and authenticity. Real agonising case histories have been woven in docudrama-style. Black beautifully portrays a sturdy soul suddenly destablised, her chignon always neat but her conversation growing flustered. Steven Webb is brilliant as her spiky, sensitive other son, and Michelle Tate's Emma – motor-mouthed and spasmodically abusive – is frightening and vulnerable.

Finally, The Pitmen Painters turns out to be by far the best in the National's current run of biodramas. A delightful transfer from Newcastle's Theatre Live, it was written by Lee Hall of Billy Elliot fame. In many ways, it covers similar ground, with a nod to The Full Monty into the bargain. It tells the story of the Ashington miners: a group of working-class northerners who, in 1934, determined to take art classes, hired a posh Royal College-educated tutor, Robert Lyon. They proved startlingly talented and caused a stir.

Director Max Roberts' actors joyously bring to life salt-of-the-earth characters whom you feel you know and love. Deka Walmsley is on top form as the fulsomely bossy George. Ian Kelly is good on the tutor's flashes of snobbish insensitivity and a stricken tenderness for his favourite pupil which he never quite manages to express. The collective debates about the meaning and value of art are explosively funny and tetchy, before they grow more serious. One or two long speeches do sound like elementary didacticism. Yet Hall keeps the opinions conflicting, raising far-reaching questions about aesthetic presumptions and personal prejudices. What's more, The Pitmen Painters turns into one of the most moving laments I've heard in years for the old socialist values that died with New Labour.

'Marguerite' (0870 040 0046) to 1 Nov; 'The Long Road' (0870 429 6883) to 5 June; 'The Pitmen Painters' (020-7452 3000) to 25 June