I am pretty used to writing Gradle build scripts in Groovy. Therefore, I know some basic stuff, but I never used Groovy for anything else.
Groovy is as clunky as I feared. It really feels like somebody saw Java and though "variables and lambdas are too verbose" and then just threw some of that stuff out. It's usually just a thin wrapper around Java and not even good at it.
I really prefer Kotlin over Groovy, although I respect the use of Groovy in Gradle build scripts. Groovy is ok-ish as a scripting language - it's just bad as a programming language :P