Basically Rust is a slightly more pleasant C++, but still huge, complicated, things break all the time, and there's no IDE support to help you make sense of anything. It's probably more robust, maybe faster as things get big, but I haven't got there yet.
Nim is as easy to write as Python, the toolchain is very easy to set up, creating Nim interfaces (with documentation) to your favourite C or C++ library is dirt simple (thanks to tools that come with the compiler), and the language is shockingly fast.
Right now, it's just so much easier to get things done with Nim. Reminds me of Coffee-Script - because it compiles to another language, you get access to a million libraries and platforms for free.