From an arch user's perspective (mine), Nix seemed like Arch but better, with a double release model (that is, both fixed release, and rolling release, which I like a lot), and Nixpkgs seemed like the better AUR with builtin caching. Also https://devenv.sh peaked my interest. Not only that, but I was just curious. So... I wanted to install NixOS.
I'm not much of a distrohopper, but with a separated home partition, I thought, What could go wrong?
Having already used it on a dedicated server (and wasting... an hour of.. paid.. KVM access...) and, I have to say, with great success, I was very happy to try it on my desktop.
I have to say, the NixOS experience is great. Apart from me being stupid and f.cking up hardware-configuration.nix (/home/ilya/.nix-profile -> /nix mount, specifically), it is amazing. Add a package, rebuild. Done. Add gdm. Rebuild. Start gdm. Done, you now have a GDM configured out of the box. It just feels like magic.
Also, NixOS is as magical on servers, as on desktops. Make a simple NixOS module for a PHP app, and BOOM! it's running! Want to be fancy and include a game daemon that has impurities and writes to the config? Easy, systemd declarative configuration gotcha. Set RuntimeDirectory, copy the configs to there and start that demon! (haha get it because daemon...)