There hardly any even more over-hyped buzzword that "Reactive" (aggressively marketed by Typesafe investor's money). Well, only "Bitcoin" has more hype.)
For a quick glance everything is very clever. They position themselves (in rather very politically correct wording) as finally a fix for that horrible mess called Java. Not only that, they, it seems, came with "innovative" solutions based on proper concepts and paradigms.
They use Scala language (ignore the "scalable" meme, think that it is a functional languages with advanced type system (a-la Haskell) which compiles into JVM bytecode and has easy Java interloop, so you could call your crap). Being functional and well-designed by prominent academics, it really allows to use order of magnitude ;) less lines of code to express the same ideas.
Not only that, they also "re-implemented" the proper concepts (Actor Model, Message Passing, Fault Tolerance, Light-weight Isolated Processes, etc.) pioneered by Erlang which was the first functional language "properly" designed designed for concurrency. They call it Akka.
And, finally, there is a MVC web-framework - Play!.
Well, I was hyped and decided to take a look. But there are no miracles in Java world.)
Almost 250Mb of compressed crap (jars are zip archives too) with is supposed to be loaded into JVM, which, remember, is just an ordinary, user-level multi-threaded process, which tries to manage memory, threads, synchronization by itself (which is an OS job) and that means only problems.)
So, I supposed to load about a one-third of Gigabyte of compressed crap into a JVM instance, which will waste at least 2Gb of RAM in order to have a few nice things?
No, thank you. I will use Erlang.
btw, I could easily understand all the excitement of those pointy-haired bone-headed managers, inhabitants of the Java world - for them wasting machine resources and profound inefficiency when it comes to communicating with the outside world (JIT-ed native code runs quickly) is only source of bigger budgets, staffing and, you see, a few more years of getting salary for projects that will fail.
But this is the best thing we have today.)