There is so much to love about Elm. It is a typed language, so it eliminates typing issues, like 1 + "1" = "11". Its compiler is great. The compiler catches almost everything and offers easy-to-read suggestions to fix your code when there is a problem. Elm's compiler virtually eliminates runtime errors; at least I've never had a runtime error with Elm.
I also like the debugger. It allows you to easily capture your steps as you click around your application, save those steps into a file, and send that file to other developers, which allows them to run through your steps on their own machine; seeing Elm's output at each stage. It works like a "steps to reproduce" bug report, only automated, which makes finding and fixing difficult bugs easy.
There is a lot of good documentation for Elm as well. Elm's documentation itself is good. Manning and Pragmatic Programmers both have good books on Elm (both are still early access versions though). Pragmatic Studio also has an excellent video course on Elm for about $60 (https://pragmaticstudio.com/courses/elm), if you're interested in learning it.