As you enter the installation, you follow the sweep of the aptly-named 'Curve' space of the Barbican, drawn in by the gradually lifting light levels and growing noise of rushing water - turn the corner and see a wall of rain. A black grid of heavy downpour lies ahead, but miraculously, as you walk slowly through it, the water stops around you as you walk - and you stay dry as if in your own personal forcefield space. It's not simply like walking under an umbrella - you pause and look up in wonder that there is nothing but air above you.
Yes, there are limitations to the (considerable) technology invested in the piece - if you walk too quickly, you won't beat gravity, and rain already in the system will soak you; droplets continue to fall in some areas; if you are wearing too much black the sensors won't pick you out as clearly - but all-in-all there's something quite uplifting about walking towards the powerful light on the far side of the installation, picking up shimmering light through the droplets all around you.
I'm not convinced I'd have been quite as happy had I queued for several hours. Perhaps a comparable experience was Gormley's 'Blind Light' at the Hayward a few years ago, which drew similarly huge queues, even just to get into the exhibition, before you faced queueing again for specific elements of the show. This seemed less substantial - Gormley's piece was incredibly immersive, but here, while the technology is deeply impressive, it remains a little too similar to daily experience of huddling in a shelter from the rain - although of course the interaction is the draw. Both share the same value in watching others as they interact with the piece - our group seemed to spend more time doing that than wishing to walk through it again themselves, which is telling perhaps.
I was fortunate to be at an after-hours event hosted by Love Art London, so had the benefit of skipping the queues, and getting to hear design collecive rAndom International talk about the premise for the piece, the inspiration behind it, technological difficulties they encountered, and their upcoming work. Particularly interesting was conversation on the programming of empathy into technology. I'd urge you to check out their TED talk too.