It feels pretty familiar. It's fairly concise. Seems easy to introspect on, if you need to. I'm guessing it made it a lot easier to generate the gorgeous doc available in their API Documentation application.
On the downside, some ugliness seeps through. "super" calls. Primitive Types vs. Reference Types. Remembering to use commas, in general, since the class definition is largely a bag of object literals in object literals.
'window system' vs. 'page' GUI - Running the demos, it's clear that this is a toolkit to build applications that look like 'native' applications - a typical GUI program you would run on your desktop. Compared to the the traditional 'page' -based applications that we've been using since we've been surfing the web.
This is of course a contentious issue. Uncanny Valley and all that. Still, seems like there's potentially promise here, for at least certain types of apps.
Here's some rational on the non-CSS-based styling.
The downside I see is that the API is fairly large, and without syntax assist, I can see that you'd be keeping that API doc open all the time to figure out what methods to call. This style of programming also seems more relevant for 'window system' UIs compared to building typical web 1.0-style 'page' UIs.
Test Runner - 'nuff said.
lots of documentation - I couldn't find any kind of introduction on the widgets in all this though. Still, this level of documentation seems to be above average, relative to other toolkits.
Anyone else played with this?