They're not all bad. My current favorite is the Firebeetle from DF Robot. At $6.90 a piece, comes with a JST 2.0 connector for a 3.7v lipo battery and, more importantly, runs using 10 μa in deep sleep easily. (Measured on multiple boards). Finally, is well documented and has great support from the supplier.
Nice high level overview of the language differences. I'm surprised they don't have reified type support for inline functions as something that Kotlin has, but Java does not. Very useful in providing cleaner method invocations where inline functions are an option.
I've heard the argument that it's all just syntactic sugar, but then again, every single turing complete language is also just syntactic sugar over programming with bits. The advantage of Kotlin is the ability to write less, but more readable code that is safer from NPEs. Oh, and it's much more enjoyable to use!