Man and Superman, National Theatre

How do you take your rom-coms? Full-fat Hollywood schmaltz, Shakespearean, or lean and elegant – a Stoppard perhaps, or Coward? If your answer did not include “With lashings of social philosophy, ethics and a lengthy dream sequence, preferably running north of three hours”, then Man and Superman might not be the play for you.

For those who prefer things quick and contemporary there’s Closer up the road at the Donmar, but for anyone prepared to take a risk with an Edwardian oddity – a baggy, generous, thinks-faster-than-it-can-talk comedy – Shaw still has plenty to say.

At full length, George Bernard Shaw’s Man and Superman – not a play at all, according to Shaw, but “a comedy and a philosophy” – runs at over four hours. Thankfully, director Simon Godwin has given it a bit of a trim, cutting things back without losing the play’s greatest oddity of all, the Don Juan in Hell dream-sequence that makes up the better part of Act Three. Cut at the premiere and most often since, it’s the bloodless philosophical heart of a romantic comedy that would much rather talk than embrace.

Fiennes brings a mania, a physical restlessness to proceedings

Shaw’s premise is simple: the Don Juan story is updated for his own times, but with roles reversed. The Don himself – here transformed into one recreational revolutionary, Jack Tanner – becomes the hapless victim of scheming women, rather than their seducer. It’s a story that takes us from rural England to Spain, encountering Brigands (with strong socialist convictions) along the way. A substantial detour to Hell sees the characters revert to their legendary selves, pitting Donna Anna and Don Juan against master-debater The Devil.

There’s an easy, unselfconscious neutrality to Godwin’s modern-dress production. The relocation privileges concept over context, stripping away period fluff and gently pointing up the pertinence of Shaw’s social commentary. It’s a shift that offers little in modern specifics however, anchored as the play is by the moral codes and societal expectations of a different generation, a different world. The joy is in the details: the opening strains of Radio 4, our hero a guest on Desert Island Discs; the Heavenly lift that makes a satisfyingly earthly “ping” when it arrives; the ghetto-mockney chauffeur.

Jack Tanner/Don Juan is the motor that drives this wordy drama, and it’s one speeding smoothly in Ralph Fiennes’ hands. What a pleasure to see Fiennes in a stage comedy after Hamlet, Oedipus, Brand. He seizes on this amateur anarchist with urgency, bringing a mania, a physical restlessness to a role whose natural habitat is the page, or even the radio, rather than the stage. His age, however, entails a rather older cast than we might otherwise expect.

It’s hard to believe Indira Varma as a girl still young enough to require a guardian. Her authority, her physical presence is not one of youth, despite some lovely mannerisms, and it’s a shift that can’t but unsettle the politics (sexual and otherwise) of the whole play. Ann and Jack are not some Edwardian Beatrice and Benedick, scrapping amorously in middle age, indulged by all around them. They are each revolutionaries, fired by the extremes and passions of youth – by politics, power struggles and what Shaw euphemistically terms the “Life Force”. They have to believe, or else how are we to? A final scene that reads as tragicomically serious here becomes farce – elegant and impeccably executed, not perhaps an ending to match the scope of the preceding three and a half hours.

Nicholas le Prevost splutters and expostulates beautifully as resident conservative Roebuck Ramsden, while the wonderful Tim McMullan (pictured above) brings charisma and countless laughs in the gift role of The Devil/Mendoza. They lead a supporting cast who catch and match Fiennes’ energy throughout, aided by Christopher Oram’s clean designs and some pulsing remixes of Mozart’s Don Giovanni from Michael Bruce.

It’s hard to imagine Man and Superman being staged much better, but whether that’s an argument for fighting for the scarce tickets remaining for this production, or simply staying at home to read the play instead is unclear. Fiennes’ performance is a memorable and a joyous one, an unlikely romantic lead who wins both the audience and the girl. A theatrical Superman? Perhaps.

• Read more theatre reviews on theartsdesk

MORE GEORGE BERNARD SHAW ON THEARTSDESK

Mrs Warren's Profession, Comedy Theatre (2010). Felicity Kendal in plodding revival of Shaw's take on prostitution

Pygmalion, Chichester Festival Theatre (2010). Rupert Everett's sulky Higgins is outsmarted by Honeysuckle Weeks's Eliza (pictured)

The Doctor's Dilemma, National Theatre (2012). Tragedy is the spoonful of sugar that helps this medical satire go down

Widowers' Houses, Orange Tree Theatre (2014). A timely revival of a timeless satire

The Philanderer, Orange Tree Theatre (2016). Modern-dress Shaw is resonant but long-winded

Saint Joan, Donmar Warehouse (2016). Revival of Shaw classic is a tour de force for Gemma Arterton