Few months ago I decided to try something different, like different platform and different language. As I mostly work with Python/JS/JVM langs, I chose .NET and F#. So I read The Book of F# by Dave Fancher from Joy of Coding bundle. And it was interesting. In the book aspects of F# are nicely explained with examples. Also book covers non-straightforward parts of the language, and explains why it was made that way.
Although author of the book assumed that readers would be familiar with .NET platform and C#, it wasn’t a problem at all.