I found String (Boot) a horror to work with. Annotation based devt with super weird errors. The great thing was that most errors where run into by many before me so could be solved by a simple web search/ Stack Overflow article.

To me being able to CTRL-click my way into the libraries is very important. Overuse of annotations (a.k.a. magic) breaks that. It is what monkey patching is for Ruby. The beginning of the downfall IHMO of an otherwise great language.

Luckily Kotlin's culture avoids this.