I have to say that that "surprisingly simple" thing is happening more and more for me on NixOS as well.
Recently a customer wanted me to use Fedora (I never visited the RPM side of the world before), and after truly the worst installer I've ever used, the actually system was nice. I do like Cockpit.
But then I needed to install an initrd that would me unlock the full disk encryption via SSH (it's a remote headless box). It took me half a day and a forum post to get it to work. I wrote a full page of notes for next time. Then the Firewall: I hit a bug (plus user error) which left me wrestling with a non-existent Tailscale interface for a while (it warns you for non-existing interfaces, but not with only a case mismatch, it then lets you do everything as if the interface exists), but after some hours I was done setting the zones, another page of notes and commands to enter to get to the desired state.
These configurations are both 1 or 2 lines in a NixOS config file. And that "work" is now done for all my NixOS servers.
You could argue that NixOS hides a lot of complexity, but so do Dracut and Firewalld of course. Nix is difficult, it's a high level abstraction. But it also just a bunch of key-values, and write-once, deploy everywhere.
The difference is, you can create proper abstraction modules that put everything together, from dependencies, to config files, firewall rules etc and have nice options for your abstraction.
No other system provides this in that sane way. I used countless configuration systems, from custom bash hacks, ansible, chef, puppet, salt - I have seen a lot.
Nix is just on another level. Never going back
Yeah once you've used Nix[OS] and home-manager, it's hard to go back to apt or brew or the dreaded "sudo make install" without feeling like you need to have a shower afterwards. And I was a loyal Ubuntu person for like 15 years. It's especially true if you're a dev installing and uninstalling all day long.
This has been my experience as well. Before I switched to NixOS I used ubuntu for 2 years. I never grokked the ways of apt and how or why it would "randomly" brick my system in some way. With NixOS this has never happened. `nix-shell` is dead simple, adding packages to environment is dead simple, never has it bricked my system. The hard part of NixOS is if you want to do advanced things with the actual nix language, and of course the horrible error messages.
In terms of all the linux systems I have used, NixOS seemed to least magical to me in terms of what is happening under the hood.
>> You could argue that NixOS hides a lot of complexity
They both have the same complexity in that scenario. Underneath it's very comparable configuration for both but Nixos provides an easy abstraction for that specific case.
If you can stay on the happy path with nixos then it's pretty lovely. I've even adopted nix-darwin for my mac's too.
I'd still deploy Redhat/Fedora over nixos on anything revenue generating though. The problem is when you have to come off the happy path in nixos and now you're debugging some interestingly written c++ code that evaluates a language that has a derivation expressing what you wanted done. Contrast with the redhat situation, it's simpler but less convenient in the general case.