No parsing query parameters in servlets! No formatting Strings! More powerful than JSON in "regular" Ajax, because you can send the behavior of objects, not just their state. Almost like using RMI in regular Java. This is one of the, possibly THE, best feature of all of GWT. See http://courses.coreservlets.com/Course-Materials/gwt.html for the complete GWT tutorial series, associated code, exercises, and exercise solutions. That site also lets you download PDF files of each lecture, for saving or printing.