We are using Kotlin since 2015 (long before Google announced first-class support for this language). Back in the day we almost immediately fell in love with such features as lambdas, null safety, data classes, functional programming constructs and others. In more recent years we very much enjoy other major features - for example, Kotlin coroutines. Nowadays our Android application codebase is fully migrated to Kotlin, we don't have a single Java language file written with our hands.