I agree for your personal computer. I've been using it on my PC for several months, and it was definitely a mistake. Most things work fine, but there are enough problems that it is extremely noticeable. Whether it's the mess that is steam-run and that whole hack, or having to build your own derivations for literally anything that's not widely used or that you need the latest versions of, it's just an endless time sink. And the documentation is non-existent, as you say. You need to go into the git repo to see what actual options are available, despite how comprehensive the options search on the NixOS page looks, it's not.

For a server, where you're typically doing that kind of work anyway (and want to have the specificity and control), I'd say it's pretty good (Guix works too).

I'm actually going back to Mint today.