Thanks for that information. I used GWT on two personal projects years ago and for customer work three years ago. The only thing that I didn't like we're the long build times.
I like web dev environments that use the same language on both client and server sides: Meteor, Clojure + ClojureScript, and GWT. I need to use several programming languages and there is always a small overhead for me when switching languages.
It's not exactly been bleeding edge the past few years. Now with the 2.7 release and the 3.0 release (which is hopefully coming very soon) it's receiving a major revival.
One of the most important new features are javascript interopt, which enables you to write libraries in java and let other people use it like any other js library. In the other direction, you can easily use javascript (libraries) in java.
That means it's possible to just use modern stuff like polymer from within gwt without much of a hassle.