Java 9 might not be adding major changes like Java 8 which had features like Lambda or Streams or Interface modification, but it does have some good additions.
JShell: If you have worked in python or ruby, you might be aware of shell features these languages provide to quickly run and analyze commands and snippets. Java has come up with similar shell as JShell in Java 9 where you can evaluate the system.
Java Modules/ Jigsaw: Java has taken further step towards modularization. You can define your application in forms of modules and tell JVM what all modules will be used by current module, and what all modules will be exposed which can be used by others.
Private Methods in Interfaces: Java 8 gave us liberty to add method definitions in form of static and default implementations. With Java 9, one can add private methods to help us with organising our code better.