I've been developing in Scala for years, but lately I've really grown sour at the TypeSafe/Lightbend libraries and tools (poorly documented, half-implemented libraries with major breakage on each release with little to no migration documentation).

People like Paul Philips (yes yes, I know he's ranty and rubs people wrong and is kinda intense, but he makes good points) show that you can build a sane language on top of the JVM, but Scala makes a lot of the same concessions and refuses to fix a lot of implementation bugs in favor of backwards comparability and enterprise support.

I wrote Kotlin off originally as a late into the game pull by Jetbrains, but now I really want to take another look at it and see what type of library and JVM support is has.