So are many of the existing underlying JVM features today - most developers don't use them directly. However they do use the features they enable all the time.

So are many of the existing underlying JVM features today - most developers don't use them directly. However they do use the features they enable all the time. Personally I think Truffle/Graal are by far the most exciting features in Java 9. They'll enable really amazing innovation in all sorts of JVM languages.