I really like the conciseness of this syntax. The language seems very well thought through.

That being said, I've been working with NixOS recently and it's made me reconsider what is useful for a configuration language. In many reasonably large software projects, where configs become very complex, config reuse (in other words templating or meta-configuration) becomes an increasingly helpful feature. Nix configs are great because it's not just a config, but a full blown purely functional language for manipulating the config. It's intuitive and powerful once you get the hang of it, and I sometimes find myself wishing I could use it when I have to work with yaml, json, etc.