> auto generate sensible [...] 'hashCode' methods

Unless you're using arrays. They went with "predictable" over "sensible" here.

> is flawless from my experience

As a heavy Kotlin user, I'd say it's far from flawless (not sure if you mean interop or the entirety of the language, but applies to both). I'm often creating and starring YouTrack issues. But yes, it's still a highly recommended alternative to Java.