Key highlights as stated by Guillaume:

- a static type checker to let the compiler tell you about the correctness of your code,

- static compilation for the performance of the critical parts of your application,

- modularity, splitting the Groovy JAR into smaller feature-oriented JARs and letting you create your own extension modules,

- JDK 7 Project Coin syntax enhancements, so that Groovy is still as friendly as possible with its Java cousin,

- and JDK 7 Invoke Dynamic integration to benefit from the support of the JVM for dynamic languages.