I have microservices in production using both. Kotlin the language, I absolutely love. I'd put it in my top 5 languages. I don't hate Java but I've never really enjoyed writing it. Even with all the cool new features, it's always felt bloated to me. I can't see that ever going away.

With that said, I really hate how tight of a hold JetBrains has on Kotlin. While you may find an outlier here or there, (someone using Eclipse/NetBeans - heck, I've even used Visual Studio Code and Vim to hack on some stuff) 99% of the people writing Kotlin are using IntelliJ. Kotlin is built to sell IntelliJ. (And the lock-in is pretty apparent) I don't begrudge a company the right to do this. I don't like it, but I have a choice whether or not to use the language.

Lastly, Kotlin feels unencumbered. One can program in a functional style like Scala. One can program in an OO style like Java. It feels "free". The sugar that it adds to Java makes my day to day a pleasure.

So consider me a fan of the language itself. I highly recommend building things with it. Am I optimistic about its future? That's really hard to say. Google's behind it at the moment, but Google's attention span rivals that of a fruit fly.

I sometimes think that Kotlin as it is, could not exist without Intellij.

[1]: https://github.com/udalov/kotlin-vim

[2]: https://github.com/JetBrains/kotlin-eclipse

[3]: https://github.com/fwcd/kotlin-language-server