I mentioned Cocos2d-html a few days ago, a HTML5 port of the popular Cocos2D game library, they released a tech demo showing the game in action, Moon Warriors.
I'm not sure how well that will embed within my blog software, so if you have trouble playing you can open it directly here. You can control it using the standard WASD keys, simply click the app to start ( or reload this page to stop ). It was released under the GPL and you can download the full sources here.
As you can see, it’s a capable library and if you are interested in HTML5 game development, is certainly one to consider!