Nelson Minar says that "calling it Chrome Angry Birds is missing the point because what's really interesting is that it's a real-time multimedia cross-platform HTML 5 app" and he's right. Angry Birds works well in Internet Explorer 9 and even in Firefox 3.6, but there are some upcoming features that will only work if you install the Chrome app: for example, in-app payments.
CNet reports that "Rovio has built some special levels available only for the Chrome browser and the game includes some Chrome-specific tidbits like Chrome rocks, flowers, and clouds. Rovio will use the new in-app payments from Google to allow users to get to premium levels." Unfortunately for Rovio, a Web developer found a way to unlock all the levels injecting a very simple JavaScript code.
The game caches most of the resources, so you can play it offline.