The most common critiques I personally see are that the syntax and language is unappealing for many folks, and that the docs are pretty frequently some combinat

The most common critiques I personally see are that the syntax and language is unappealing for many folks, and that the docs are pretty frequently some combination of sparse/haphazard/stale. In my time I very often had to go read raw source to understand how to properly use some less-trivial constructs. I have enough of an FP background to find the language tolerable but not yet pleasant, or even particularly capable. It's absolutely a fair thing to not enjoy. The other major criticism that I think is even more defensible and less subjective is that incremental adoption is not very fun. Many things that are well supported on a mainstream Linux distro will not work OOTB in NixOS until some kind soul contributes the Nix-specific implementation of that thing. In some cases that's not even fundamentally possible. So you run into lots of cases where the first hit on a Google search will solve this thing if you're on Debian, but you're looking at hours of triage to do the same thing on NixOS instead. I have plenty of examples about things that are uniquely possible with NixOS too, but I don't like to evangelize anymore.