Do not let the "shell" in the name fool you. Nu is a full on programming language. I've spent more time with it than pretty much any other lang and if I have to describe it in one sentence, I'd say: It's the most beautiful combination of the ease of Python, strictness and ergonomics of Rust and of course shell capabilities of Bash.
It's really its own kind of thing. It's definitely not just another shell.
I've written very impressive and very complex software in nu. I fully expect it to take off very fast as it nears a stable v1.0. I can't imagine going back to anything else.