A great feature is the 'Appcelerator in 5 Minutes' demo. If you need 5 minutes with it to 'get' it, you're a little slow. You can pretty much learn the model in 60 seconds there. The rest is seeing the scope of functionality.
As with anything, there are applications that this approach works well for (Gmail -> GWT takes an all in one approach, but does treat the browser as a 'real' deployment environment), and many it does not. If nothing else, Appcelerator is on my list to spend some more time with.