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.