I really like Clojure and I keep coming back around to it every few months. I started playing with Clojure just a few months after Rich released it. It was one of the first open source projects I ever donated to. I always dream about working with a game engine that can be coded and updated live from a REPL.
jME3 seemed like a cool engine to start playing with and has good documentation. jMonkeyEngine 3 is a 3D game framework for the JVM. You can use it to create 3D games that run on multiple platforms.