What’s the first thing that comes to mind when you hear the phrase “3D occult mystery film opera”? Because I’ll bet that whatever this makes you imagine is nothing like the reality of composer/director Michel van der Aa and librettist David Mitchell’s Sunken Garden, which debuted at the Barbican last night. That is, if “reality” is really an appropriate word for this work, which frequently pushes the term to its limits.

Sometimes brilliant and always perplexing, Sunken Garden traces the disappearance of two people (Simon and Amber) through the eyes of obsessive documentary film-maker Toby, who gains sponsorship for a film about the disappearances from a mysterious woman named Zenna. All four of these characters, and also a second mysterious woman (Doctor Marinus), later turn up in the titular sunken garden, a place of great beauty. We learn about the troubled pasts of the characters, and they are faced with choices concerning whether to return to reality, to perpetuate their limbo-esque existence in the garden, or to die. The many issues touched upon include memory, immortality and guilt; it’s certainly a more thoroughly literary creation than the average opera.

What’s really remarkable about it, though, is the way it all comes together. The first section alternates live, sung action with spoken video clips which are to be part of Toby’s film. The sunken garden itself, filmed at the Eden Project in Cornwall, is in a remarkable 3D, with the “missing” characters holograms within it and the other characters live on the stage, though sometimes interacting (or trying to) with the holograms. It’s a trippy experience, but on occasion a breathtaking one, and the technological aspects have been very firmly welded into the dramatic concept, ensuring that claims of gimmickry are easy to refute.

Van der Aa plays similar tricks on us aurally, mixing live music with synthesised sounds, and sometimes integrating noises from the films into the orchestral texture. There’s a wonderful moment when it’s revealed that a soft clicking sound that pervades the first few scenes is taken from a moment in one of Toby’s films, in which a character nervously flicks his fingers against a business card. But the score isn’t just a box of tricks: it’s dramatic at times, almost traditional at others (the vocal writing especially), and always carefully attuned to the text. It’s also virtuosically diverse: van der Aa is renowned for his eclecticism, but he really outdoes himself here. Most impressive for me were the sections of music depicting Amber, a rich student with a fondness for clubbing: van der Aa blends elements of dance music into his score with astonishing effectiveness and sincerity.

For all the various ways in which this opera is completely radical, however, it has one shortcoming which is a real operatic chestnut. An awful lot of crucial information regarding the plot is compressed into several minutes and sung incomprehensibly. This left me high and dry in the later stages of the piece, and I think that it’s indicative of the plot overall just being too complex for effective operatic treatment. There’s a fascinating story here, no doubt, but it really needs a slower pace and more fully developed characters (it’s tempting, and almost justifiable, to make a joke about the characters having fewer dimensions than the film). While the conceptual side of the opera, including the integration of its technological aspects, felt nigh-on perfectly planned out, as a dramatic piece it didn’t quite cut it.

That said, it was delivered with enormous passion from everyone involved. Roderick Williams, Katherine Manley and Claron McFadden were the three live singers, and all sounded excellent, complementing each other and (except where it mattered most) projecting the text clearly enough that surtitles were not missed. On screen, Jonathan McGovern and Kate Miller-Heidke were required to act as much as sing, and they did so convincingly, McGovern’s closing lines memorably delivered. The ENO Orchestra sounded very strong in the pit, precisely directed by André de Ridder through every tight corner. Technically, this must have been a monumental effort, and a hitch-free opening night is a brilliant accomplishment for a work of this level of cross-media complexity.

Is this the opera of the future? I’m not fully convinced – for one thing, the technology will surely date fast, and so will the trendy contemporary references that fill it to bursting (iPhones in chic pink covers, references to doped-up cyclists). We’ve also recently seen in London, courtesy of George Benjamin and Martin Crimp’s wonderful Written on Skin, that opera can artfully traverse the line between the real and the fictive without using any video technology at all. But Sunken Garden is nonetheless a truly remarkable artwork which deserves to be seen and heard, and which merits the attention it’s already received. And when else are you going to get to see a vertical pond?