I tried NixOS once and the overall impression was: it's magic. I mean, you know, when you are installing tools on relatively "clean" distro, like Arch, there usually something fails, and you have to try this and that, tweak something, and it is good old "linux way".

And NixOS is something so elegant and beautiful, so mathematically "right", that I subconsciously expect that it wouldn't actually work, and yet it does. I tell it what I want to get (relatively marginal configuration, btw) and it configures installation just right. I break something and it rolls back without a problem.

So the main question I've had ever since: why this stuff isn't popular enough yet.