We have started using it for our dropwizard projects. It has been pretty great. The biggest thing about it is that there is pretty much no friction for existing libraries so far.
We’ve avoided using any Kotlin specific libraries other that small wrappers that add extension functions (for things like jackson and JDBI). This has been a huge win since our teams have continuity with libraries but a better language. Have yet to run into any issues that were not trivially solved
That is the biggest thing for me, there is not much to write about because everything we use pretty much just works out of the box with very few changes from how we did it before