With all the buzz about Halo 3, Microsoft couldn't help but to use it as an excuse to make users download SilverLight. It is not really a showcase though, as it does not do anything an experienced designer could not already do with Flash or even straight HTML/JavaScript.
It does however demonstrate the same fundamental flaws that Flash did. Specifically, you do not get bookmarks. I would love to provide you a link to the new character images, but the best I can offer is the gateway page, http://www.microsoft.com/silverlight/halo3.aspx.
This brings in the question the usefulness of SilverLight in traditional web sites. While bookmarking does not matter for "applications" like the web-based email clients GMail and Hotmail, they are essential for "informational" sites. To solve this, Microsoft needs to find a way to continuous update the URL to reflect what is happening on the screen.
This is not the first time this issue has been raised. Flash has the exact same problem, which has reduced its use to widgets, advertisements, and games. While sites composed entirely of Flash do exist, they are few and far between and SilverLight may be destined for the same fate.