I know what GWT is. I agree that it provides out of the box certain functionalities that require a bit of "glue code" when using other frameworks.
However, the whole "just write a desktop app and we will turn it into a web app" philosophy doesn't seem very web-oriented to me. Yes, it works, it's easy, but if one day you want to change your client-side code (i.e. use a different framework or something) you'll most likely have to change the server side as well. It just seems to be too RPC-centered and too monolithic. But maybe I'm wrong.
You can do standard REST, or whatever you want with GWT. IMHO what really sucks with GWT is the language; Java really sucks sometimes and its full of ceremony. Also, I think they made the same mistake that the Swing guys did: they provided for a toolkit but they didn't provide a framework, ie, a standard way of putting it all together.
Anyway, you can check what the jBoss guys are doing with GWT, looks good even for Java: http://www.jboss.org/errai I think that if Java ever gets proper closures it will may be more of an acceptable solution for some cases.
However, the whole "just write a desktop app and we will turn it into a web app" philosophy doesn't seem very web-oriented to me. Yes, it works, it's easy, but if one day you want to change your client-side code (i.e. use a different framework or something) you'll most likely have to change the server side as well. It just seems to be too RPC-centered and too monolithic. But maybe I'm wrong.