Exactly, not just the language all the tooling (jvm tools) and IDE are also top notch. Really waiting for the new compiler frontend, which brings huge improvements to compile time.

Where did you get that info about patter matching?. By the way, java is really catching up on that.

https://github.com/openjdk/amber-docs/tree/master/eg-drafts

I agree. Kotlin is insanely comfy to program in. Lots of convenient features, good design, doesn't force annoying OOP boilerplate or FP constructs on me.

What other languages have you worked with? I enjoy Kotlin, but also think Swift (from my limited experience) and C# are wonderful.