I find flash very attractive from a user's perspective: you open up the game website, click "play" or something and then you can play the game - it just works. Flash is installed everywhere, why not trying to use it as a way to bring a game into the browser, like it is done with Adobe Alchemy and that Unreal demo. For instance, I did some research for a potential client and tried a game she pointed out: it was so well done and addictive, I caught myself playing it for 3 hours. One reason was that the gap between finding the game and actually playing it was merely nothing.

What about Silverlight 5? XNA 3D support was now added.