...and it's stunning. Seriously. It's actually three separate features in one. First, all the audio is outside of you rather than stuck between your ears. Second, it's surround sound so that dialog actually comes from your iPad, while music comes from all around. And third, it tracks, so if you look left the dialog all comes from your right AirPod -- and it's positively disconcerting it's so real. I thought for a second all the sound was actually coming out of my iPad and, oh crap, I have to turn it down not to bother the neighbors! Before realizing... oh my god it's actually that realistic.
So not only does it blow me away technologically, but also that I got it as a free upgrade almost a year after buying the headphones! People love to criticize Apple, but man do they do some wonderful things for their customers.
Now I'm just so disappointed the feature is iOS-only, and not for Macs. I watch all my TV on a projector hooked up to my Mac, and man... if I had spatial audio while viewing that... I can't even imagine. It would beat any movie theater I've ever been to. (And sadly, iPad HDMI output is low-quality, as it heavily compresses the output.)
My understanding is they don't support Macs because they don't have accelerometers/gyroscopes so the AirPods wouldn't know what they were relative to spatially. But man, I'd be happy just for a button I could click that says "my head is looking directly at the screen now". Wouldn't that be enough? But there's no mention of it being in Big Sur, so oh well...