There's lots of criticism about the Nix expression language, but it's way overblown IMO. The core language is small. It's essentially just JSON with functions,

There's lots of criticism about the Nix expression language, but it's way overblown IMO. The core language is small. It's essentially just JSON with functions, very similar to Jsonnet. But with Nix, people make too big of a deal out of implementation details like it being lazy, functional, etc. I personally like Nix as a configuration language because it's suitable for complex configurations despite it being small and simple. There's a case to be made about improving the state of the Nixpkgs APIs though. Stabilizing the APIs and documenting it more thoroughly would dramatically change how people perceive the complexity of Nix. Experienced Nix users grep the Nixpkgs repo to learn about its APIs, but that's far from ideal for newcomers who won't even know where they should look for information. Still, despite its reputation, Nix lowers the bar for software packaging. Package definitions tend to be more concise, customizable, and reusable than the competition. Nixpkgs contains many useful utilities for packaging and there's an abundance of real world examples contained in a single repo. I also frequently work with RPM, but Nix is much easier in comparison.