Kotlin is an amazing language under active development. You can write less code and make it more readable by using Kotlin instead of Java. If you are a Java developer though, you may find it a bit frustrating to switch to something new.
I think it’s always good to learn something new, expecially if by learning new things you don’t have to loose the old ones! Kotlin is fully interoperable with Java so you can start writing Kotlin code today and incorporate it into your old projects.
Kotlin alone will help you with the dreaded Null Pointer Exception, it will cast types for you automatically (where possible), you will be able to pass functions into other functions and much more! When you add all of the Kotlin specific libraries aimed at simplifying Android development, you get a deal which is hard to turn down.