The Sound of Music in Regent's Park has been the hit show of the summer. I've rarely seen the Open Air Theatre as packed as it was on Tuesday night, and Charlotte Wakefield as Maria is indeed completely enchanting. Noel Coward complained that Mary Martin was a bit long in the tooth to play a naughty postulant in the 1959 original; Wakefield's breakthrough performance, coming just seven years after Connie Fisher's at the Palladium, enriches the girlishness of the role, making Maria much closer to the children (in height and temperament) and much more surprising - she's not remotely nanny-ish - as a sex object.

And last night I caught up with the other Rodgers and Hammerstein show in town, Pipe Dream at the Union, where my colleague Mark Shenton asked me how I'd enjoyed the sex scene in The Sound of Music. I had absolutely no idea what he was talking about until he referenced the second act number, "Something Good" (for which Rodgers wrote music and lyrics), sung by Wakefield and Michael Xavier as Captain von Trapp while dangling their bare feet in the watery channel that runs around the stage.

This is indeed the song that cements their love affair, but it's no hotter, really, than the water looked. Tepid, in fact. Not much chemistry. But Rachel Kavanaugh's staging is so clever and spirited that the whole show goes with enormous zest and zing, even if the Nazi shadow over the singing competition is not as threatening as it was at the Palladium in Jeremy Sams's brilliant production.

Helen Hobson sings the Abbess charmingly, getting right away from the Constance Shacklock monster version in the original London production, which I saw - "Climb Every Mountain" was an invitation to clamber over Constance herself - although Lesley Garrett at the Palladium had a much fuller, more contralto-ish voice for that magnificent anthem, which remains untarnished, as does "You'll Never Walk Alone" in Carousel, by repeated performances and unlucky appropriations.

Kenneth Tynan described The Sound of Music as Rodgers and Hammerstein's "Great Leap Backwards", and the reviews were distinctly mixed. As indeed they were for the more experimental Pipe Dream four years earlier in 1955. This was a collaboration with the novelist John Steinbeck, a conflation of the flophouse and whorehouse worlds of Cannery Row and its sequel, Sweet Thursday.

It's absolutely intriguing, not least because there are no take-home numbers - which is not to say the music is uninteresting; there are several really beautiful songs - and nothing much happens. Well, nothing much happens in Oklahoma!, either, but that great musical leaps off the stage and grabs the audience; Pipe Dream sidles up and invites us in, which makes the sweaty imtimacy of Sasha Regan's production - hurry, it ends on Saturday - so perfect.

You won't even know the names of the songs but, trust me, "The Man I Used to Be" (sung by the romantic lead, a marine biologist who's worried about star fish), "All At Once You Love Her" (reprised in the second act by the whorehouse madame, Fauna - real name, Flora, and deliciously played by Virge Gilchrist as a Gabrielle Drake lookalike) and the final love duet, "The Next Time It Happens," are all sinuously melodic and engaging.

The Rodgers and Hammerstein licensing company's president, Ted Chapin, joined Shenton on the stage after the show last night to explain that Pipe Dream stuttered because its genesis was so fraught and Rodgers made two massive blunders. He cast an inflexible opera singer as the madame and hired Harold Clurman as the director (Clurman was an "intellectual" critic and all-rounder; his history of the Group Theatre he founded with Clifford Odets, The Fervent Years, is one of the best of all theatre books).

And then, three months after it opened, New York woke up with My Fair Lady on its doorstep and Pipe Dream faded, along with all the pipe dreams in the saloon bar of Eugene O'Neill's The Iceman Cometh ten years earlier. The title of the musical is also a puzzle; turns out that the vagrant romantic heroine, Suzy (done with an understated, tactful charm by Charlotte Scott), lives in a boiler-room stuck up a pipe. That's when she's not whoring away with the other gals, though the only real raunchiness is provided by Lizzi Gee's dynamic choreography, a splendid lingerie-clad eyeful of haunch and buttock at indecently close (hind)quarters.

Kieran Brown is terrific as the marine biologist, Doc, and there's a lovely dim character called Hazel - his over-fecund mum had run out of boys' names - who has his moment in the spotlight with his own song, "Thinkin'", which a goofily endearing Nick Martland makes sound much better than it is.

Someone walks up to him and says, "Hi, Hazel," which amused those of us who remember Hy Hazell, a great musical comedy star who kicked up her legs with Anna Neagle in the long-running Charlie Girl; in fact, the first show Rodgers wrote after Oscar Hammerstein's death, No Strings, featured Hy Hazell in the London premiere at Her Majesty's in 1963... little known fact: Hy Hazell choked to death eating a steak (Bye, Hazell).

Shenton suggested to Ted Chapin that Pipe Dream had been the Viva Forever! of its day, an insult Chapin took with a good-humoured shrug but which Viva Forever! producer Judy Cramer can only construe as a massive compliment. Shenton was intending a remark about the notoriety of the show's flop status, though Rodgers in his autobiography said that the show only suffered from the fact that he and Oscar Hammerstein had written it. Had they been a couple of unknowns, he said, it might have been better received.

He should have known by then, of course, that all great musicals rarely get unanimously favourable reviews, and Pipe Dream was and remains little more than a mood piece with music, and not music from the very top drawer. But as the Union proves, music by Rodgers doesn't have to be from the top drawer to be better than most everyone else's.

The great power of The Sound of Music - or The Sound of Mucus as those of us with heavy summer colds have been calling it this week - is the store it places by the redemptive power of music itself. Maria is a conduit of the inseparable streams of music and love, and the scene in which she instructs the children in the simplest of songs, "Do-Re-Mi", is not only a scene of genius, it is as delightful, joyous and moving as any scene in Shakespeare or Tennessee Williams.