Another valid complaint is that dev mode runs quite slow, particularly if you're developing something like a game. I read an article about how they are addressing this so that dev mode runs almost as fast as the compiled result, but can't find the link now. Maybe it's already live? Been half a year since I've used GWT.
But I second the recommendation overall. One thing I learned the hard way though, is that their widget library is pretty constraining, and a very leaky abstraction. I would consistently run up against walls using a particular widget, bang my head against it for a day or two, then scrap everything and roll my own solution. Eventually, I just used GWT to compile the core business logic of my app (which would have been a nightmare to do in JS), and did UI with the standard HTML/CSS/JS flow. Doing UI in Java is too clunky for me no matter what library I'm using though, so YMMV.
