IME Kotlin is the worst of both worlds. It's like they took every cool one-liner example from Scala and said "see, you don't need a whole functional language to do that, we can just add this piece of syntax sugar and you can do the same thing while keeping that Java feel", but once you've done that a half-dozen times you end up with a language that's actually even more complicated since it doesn't have the underlying consistent core that Scala does.