Yep, I echo this experience. It is my main desktop OS, I am very happy with it. Myself + another developer at my company both use it, and it's starting to gain interest from others, seeing as it's mostly a panacea to all sorts of environment and configuration issues.
I was pretty unhappy learning how to write the strange config language at first, but I've made my peace with it. You will almost certainly need to write a package or two, but there's a lot of active development to learn from, and lots of example to cargo cult.
Other developer here. I've been running nixos as my main OS since about November after running Funtoo for a year or so before that. My tolerance for hacking on my distro is maybe slightly above average. ;)
On the cool side: Nix is the first linux distro I've contributed to, because it's the standard "hack, fork, pull request" process that most github-hosted open source projects use these days.
The biggest thing is that you absolutely have to drink the nix koolaid if you're going to run nixos. You can't really do the normal ./configure && make && make install, because paths to libraries are all non-standard. But once it all really clicks, it's pretty great.
As far as desktop goes, the rest of this thread rings true for me too: most of the important things are there, like desktop environments, window managers, browsers, etc. There are occasionally niche/older packages that are not available. If you're willing to learn a little bit of nix language, it's relatively straightforward to add most packages.
I was pretty unhappy learning how to write the strange config language at first, but I've made my peace with it. You will almost certainly need to write a package or two, but there's a lot of active development to learn from, and lots of example to cargo cult.