The concurrency support with gpars is a really killer feature. I'd urge everyone to take at least just take a look at it. Extremely easy and made very "natural" with Groovy syntax. Yeah you can do concurrency with about every other language, etc. but this is within a JVM context.
It provides fantastic support for concurrency with gpars.
It provides the ability to write static or dynamic code.
It integrates seamlessly with Java.
I feel groovy has created it's own space in the ecosystem, continues to grow and has a bright future.