I installed NixOS for the first time a couple of weeks ago. My biggest annoyance has been that most documentation and wiki contributions seem to assume that you're running as a single-user system where it's OK to sudo as root every time you want to change some user settings.

For example, I have still not been able to run Sway as a window manager because I can't find how to set it up properly using Home Manager (doing the equivalent with an .xsession and i3 was no problem). The wiki article about it (https://nixos.wiki/wiki/Sway) has a lot of configuration at the system level configuration.nix, but most of that is missing from the ostensibly equivalent Home Manager config.

It seems like a design error that the Home Manager configuration options do not map 1:1 to the NixOS configuration options for users, and I'm guessing that error is caused by a lack of interest in properly configured multi-user systems.