I went twice to the Barbican Centre last week for two ground-breaking productions: Cheek by Jowl's Bunuelesque new version of Alfred Jarry's Ubu Roi, and ENO's 3D opera, Sunken Garden, by novelist David Mitchell and Dutch composer and film-maker Michel van der Aa.

Both were extraordinary, though the opera's book is impenetrable, but I first want to deliver some parish notes on lavatories and cakes. I could register my complaints personally to my friend and neighbour Nick Kenyon, the Barbican managing director, but sometimes these important matters of public concern are best aired in public.

I was ill on the opening night of Ubu Roi with a tummy complaint, a slightly unfortunate predicament given the lavatory humour of the text and the play's famous opening line, "Merde." I had already, as it happens, twice availed myself of the service facilities at the Unicorn Theatre by Tower Bridge, where I'd been for a matinee, and everything there was perfect: clean, well-stocked with the essentials you need in these situations and convenient.

Different story in the basement loos of the Barbican Theatre: sticky floor, unclean toilet bowls, several basins (I went along the line) without running water, no lock on the cubicle I occupied. This situation is shameful.

And the cakes in the cafe. They all look reasonably edible, but they're all - my research is based on three or four recent visits, and I've tried muffins, the chocolate and cherry, the cheesecake - all as dry as a bone. The salads can be tedious, too, but at least on Saturday night they were offering a decent pepper and mozarella option that had a bit of zing about it.

I raise these issues because I love going to the Barbican. Actually, I don't love going to the Barbican, but many of the things most worth seeing in London tend to be on there, so I think it's about time the front-of-house service started to try and match the quality on the stage and in the concert hall.   
 
Ubu is a stylish treat, as it subverts the chic dinner party atmosphere with the grotesque adventures of Pere and Mere Ubu, the modern Macbeths in an age of civil despotism and unsavoury military regimes. Film is used as a highlighting technique in the  fantasy excesses chez Ubu and a projection of inner pain and anxiety of one of the victims who wants to broadcast the truth.

It's a brilliantly worked out "concept" that doesn't suffer from conceptual hubris. Which is part of the problem with Sunken Garden, whose score is the most exciting I've heard in a modern opera certainly since, well, George Benjamin's Written on Skin, and probably, before that, since Mark-Anthony Turnage's for The Silver Tassie at ENO.

Half-way through, you put on the 3D glasses and follow the investigating hero into the sunken garden with a vertical pond, coagulant lava-like excrescences, glowing flowers and bushes and swarms of moths. Michel van der Aa shot this film at the Eden Project in Cornwall, but I found it impossible to follow what was going on, who was dead or alive and who exactly was the woman in a trouser suit who seems to be in charge.

There's one great moment when live singers and holograms are singing a quintet, and the technical configurations are masterful. Masterful, but not very dramatic. A sense of occasion soon became audibly muffled with disappointment, and the Barbican culture vultures were left snatching at straws; the music, at least is a very big straw, and so is the singing of Roderick Williams, Katherine Manley and Claron McFadden.

David Pountney, now running Welsh National Opera, was in the audience, still sporting his trademark mutton chop whiskers, and so was Pierre Audi, director of the Holland Festival (one of the lead co-producers) and founding director of the Almeida Theatre all those years ago. It was lovely to see Pierre again, and to learn that he has just become a father for the first time.

I wonder what Rufus Norris, director of the other major weekend opening (Table in the National's new black box, The Shed) will make of Sunken Garden. As the director of London Road, his pre-eminence as part-perpetrator of something genuinely new and exciting in musical theatre is still intact.

Norris was quoted in an Observer news story at the weekend as suggesting that daring new musicals could tackle any subject these days but had more trouble finding good tunes: "Think of Cabaret, Oliver! and Annie," he said, "you can hum maybe five songs from each. You'd be hard pressed to do that with any musicals of the last five to ten years."

Outside of Lloyd Webber, he's absolutely right, of course. But addressing difficult subjects hasn't been a problem for the musical theatre since 1927. Racism in Showboat, anyone? Sexual abuse in Carousel? Street violence in West Side Story? The trouble with most contemporary musicals is that they're not about anything serious very often, with the shining exceptions of London Road, Matilda and Book of Mormon; but then there's still the Norris question - who's got any take-home melodies to spare?