NixOS is great. Nix the language is just awful. I still use it for my Dev laptop and for Home Manager on all my devices.
People just seem to want to complain because it doesn't look like any of their favorite languages and they aren't familiar with functional languages. At this point, I can't imagine using any other language in place of Nix. The code would have so much noise and be much harder to read.
I mean, I'm only ever using it for configurations, and I think I'd still prefer writing Nix than YAML. I probably wouldn't like writing a full "program" with Nix, but I don't think anyone does that?
I have written a lot of PHP. In order to learn it I bought several books, I've done a dozen or so projects with it at various jobs, I've written both trivial and non-trivial things, and I have come to the conclusion that PHP is an actively terrible language [1]. It's inconsistent and hard to write in any kind of maintainable way with an ugly syntax and generally-crappy performance for any kind of logic beyond CRUD.
[1] At least version 5, which is the last version I've used. I've heard 7 is better but I'll never know because I swore an oath in blood that I would not do PHP again for less than a million dollars a year.