We're using Play pretty heavily at our startup though not for our customer-facing frontend, that's still in Rails.<p>What we love about Play:<p>* Async everything, especially the web service library<p>* JSON macros<p>* Scala-based templates<p>* Integration with Akka<p>* Support for server-sent events (we use this for cluster monitoring)<p>What we wish was better:<p>* JSON deserialization performance isn't as good as raw Jackson yet. (Our PR regarding this is actually in 2.2, should be better now)<p>* Documentation could be much better, we still have to resort to the API to figure out a lot of stuff<p>I've been using Play ever since the 2.0-RC days and it's definitely made some huge gains since then. We use Akka very heavily, especially its clustering, and Play works well in conjunction with that though there are still some gotchas lurking about.<p>Our backend is one big Akka cluster right now. We've had a few hiccups but overall it's been a hugely enjoyable experience.