Kotlin/Scala/Clojure are nice, but my experience is that just because an organization is working with Java, you shouldn't count on being able to work with some other JVM language. At my current job, we've been forced to give up on Clojure (a language I love) because the higher-ups have decided we should stick to Java.
I really hope especially Kotlin will gain more traction in the coming years, but in the meanwhile there is at least an order of magnitude more jobs in C# (where I live).
With .Net you get F#
.NET and C#/F# are pleasant and I wouldn't be opposed to going back to them, but job-wise it seems safer to stick with tried and true Java.
Regarding things that might be better I think the linq support in dotnets collections is better than the streams support in java since java has kept more old collection libraries.