Thats the magic of NixOS basically.

I've used a handfull of OSes regularly and I worked somewhere that used the Nix package manager, its pretty neat in a land of broken everything (most Linux distributions)!

Huh? All modern distris are very stable. Hadn't had problems with arch, Debian, Ubuntu it freebsd for years.

Not really, one mistake installing a package and you can have everything break. This is basically why containers/Docker and things like virtualenv exist.

My experience is the same. Rollbacks never fail. Upgrades often break my desktop environment. Maybe I should just stop using GNOME, since KDE seems to be the better supported "fat" desktop environment. Not sure if cobbling together some kind of i3wm-type environment would simplify things or result in just another kind of fragile complication.

Can't really figure out why GNOME stopped working for me after 18.03. Wish there was some kind of guide/tool for validating that my configuration.nix was still sane with newer versions.

I remember GNOME support was spotty when I used it two years ago. I returned this year to NixOS 18.09 just before 19.03's release and GNOME's been solid throughout, and I'm using 19.09 now.

I've had that break config files in $HOME in the past, but it's nothing ZFS can't deal with.