I've poked around with this. It's becoming a popular choice for Flash games, although I'm not using it myself. It's not sophisticated or even really that efficient(one object instance per tile? per particle? You can make AS3 go much faster now with Bytearray or Vector based solutions), but it's easy to start with, gives you some basic graphical features, and perhaps most importantly, is a working solution for escaping the Adobe-centric toolchain.