I find the nix language to be quite pleasant. There are some syntax quirks and types would be nice, but in general the “json with functions” vibe is imo great and a very nice fit for the domain. Lots of other modern config languages (e.g. dhall, jsonnet) have ended up in this part of the design space too.
With that said tweag has been working on a kind of nix 2.0 / nix with types for a while with the aim (I think) of being able to use it in nixpkgs: https://github.com/tweag/nickel
I also quite like nixlang for config tasks - in theory! In practice its really annoying. I think the main problem is the interpreter and the bad error messages / bad debuggability.
Part of that just comes from lazy evaluation, which makes debugging a lot harder in general (you feel this in Haskell...), but also just from nix not being a big popular language that gets lots of polish, and being completely dynamically typed.
Nix is ok. I like jsonnet more, and once I've tried to write a converter from jsonnet to nix, but it turned out this is much harder than expected (some idioms don't transfer from nix to jsonnet well.
Me as well. As a haskell / ML programmer, it is extremely intuitive. It's non-innovative (In a good way). Literally it's just a functional scripting language.
With that said tweag has been working on a kind of nix 2.0 / nix with types for a while with the aim (I think) of being able to use it in nixpkgs: https://github.com/tweag/nickel