I don't see Kotlin as a "wow" language, I see it as a "this is sort of boring but pretty nice" language like Java and Go. Maybe Ceylon is similar, I dunno. It just strikes me that Go could use a stronger competitor than Java that runs on the JVM, but doesn't seem overly fancy (Scala, Clojure) or too dynamic (Groovy, JRuby, Clojure). Kotlin is the closest I've seen to that.