I've tried it out and read the Nim book, but I'm not using it for any larger project right now. So here is a biased opinion.

Pros: Nim is about as easy to program as Python, has the same speed as C, a working FFI, and all the usual bells and whistles of modern "battery included" languages like a package manager with lots of packages. It is garbage collected, which is good -- about this, some will disagree, of course. It has nice high level constructs and doesn't attempt to reinvent OOP or something like that, the language is fairly straightforward. It also has a powerful macro programming facility, which is cumbersome to use though.

Cons: The community is too small and so far has not attracted CS people or many professionals, and there is the usual bulk of abandoned or undocumented packages you get with these kind of languages (more on that below). It has a few controversial syntax choices (e.g. identifier case rules) and also a number of semantic misfeatures that ease compatibility with C. It has support for native threads but no Green threads like Go, and consequently also no Green thread -> OS scheduling that would be ideal. (You'd like the language to do some flow and dependency analysis and parallelize to Green threads automatically, which are then mapped to OS threads, but AFAIK only few experimental languages can do that by now.) Its garbage collector is not optimal and not as performant as Go's, I believe. It uses whitespace for blocks, like Python.

Overall, Nim is a pretty good general-purpose programming language.

I should say that I have a long-term interest in esoteric languages and have been working on my own for a while. However, my main use case is desktop application development and unfortunately so far there is not a single new language that I would really recommend for developing desktop applications, unless you're fine with bindings to some monstruous web interfaces (Elektron, Sciter, etc.) and want to program half of your application in Javascript.

Rust, Go, Nim, Elixier, Julia, Crystal, etc. do not have GUI frameworks that are ready for prime-time use in production, except maybe for a few interfaces to web apps. Their native libraries (like Nimx for nim, duit for Go, Conrod for Rust) are unfinished, limited or simply too impractical, and bindings to Qt and wxWidgets are either undocumented, incomplete, or suffer from weird license restrictions (like a Go Qt binding I've taken a look at, I forgot its name). Some of the libraries also create monstrously large executables.

For command-line tools you can use any of them, just like thousands of other languages. For web programming, you can also use them but then there is also Common Lisp, Racket and plenty of other languages good for that. For desktop applications with modern GUI, on the other hand, you will be too limited with any of these languages and constantly chase some incomplete bindings or try to figure out how the bindings work. (Most docs for bindings simply assume that you've used the respective library a thousand times in C or C++, in case of which you could, frankly speaking, probably safe yourself the trouble and do it in C or C++ anyway.)

For this reason, I've decided to use Lazarus for my GUIs. Qt with C++ or Python is also a good choice. I also use Racket, but its native GUI is too limited, and still have hopes for Go.