It seems that Scala got a resounding review from the originator of Groovy, James Strachan.
I am a great fan of the concept of the Java Virtual Machine. I think that the ability to have multiple languages producing a common byte-code format produces some very powerful benefits. In essence you can have one project or multiple projects running in a common environment where code resources written in different languages can interact with each other and not be dependent on any one particular hardware infrastructure. In fact you could run your code on many different types of hardware and achieve clean interaction between them all.
That includes Java, Scala, Jython, JRuby, Clojure, Groovy, Rhino, Quercus, and many other programming languages.
That greatly simplifies the development process. Anything that makes complicated things simple without losing the power inherent in the complexity is OK in my book.
At the risk of ostracising myself on PerlMonks - I am of the opinion that perl 6 bet the farm on rolling their own virtual machine. While I know that historically speaking the JVM was not remotely open when the perl 6 effort began and what is more there was not much support for any language besides java on the JVM - but much has changed in the many years that perl 6 has languished in it's Duke-Nukem-Forever-style development cycle.
I would love to see someone implement perl on one of the open JVM platforms that exist in prove that it can be done and kept open. I would welcome it as a first step towards implementing it on the actual JVM - which is used in many many many production environments around the world.
I know that a large contingent of the perl community habitually throws stones at Java - but I belong to the subset of developers that are interested in perl and Java for the same reason - developing code with platform independence.