I recently moved back to Arch from NixOS. I really love the idea, and the execution isn't necessarily bad, but it didn't make sense for me on the desktop. Straying off the beaten path quickly led to the sense that I was going to have to learn way more about Nix than I wanted to. I hope the documentation and community grows, because I definitely got the sense that it is the future arriving early!
Unless you've drank the kool-aid, you have to learn a completely new operating system and way of doing things, a weird language that's lacking on documentation, and a ton of system or package-specific options that are even less documented, and requires you to spend too much time reading the source to understand what's going on and how to achieve something a little off the beaten path.
Feels a bit cultish IMO, and that only the illuminated ones are able to grok it. That it's my fault I'm not prepared to do the work and see for myself why NixOS is better than any other distro.