While I greatly respect the history of Java and the engineering that has gone into the JVMs of various ilk, I have to say that the restrictions inherent in Java and in the JVM and thus in most languages that target the Java ecosystem - those restrictions really suck. Kotlin sucks so far as I can tell because it is trapped by what it can/not do wrt the JVM and Java interop.

Scala tried to have the cake and eat it too, and that in my mind ended up failing in horrible ways where the whole of the suck was greater than the sum of the parts of suck. At least Scala was trying to gloriously exceed any pragmatic realistic possibly sane and mundane restrictions - but trying to break out of the JVM/Java just made Scala all the more insane in the end.

Dunno what Fantom or Gosu or Frege or &c. are like. (I do not think about Groovy much since I am bigoted in favor of (good) static typing.)