I've had a bit of experience with Struts1 and Struts2. First off, Struts1 and 2 are different because Struts2 is not a direct evolution of Struts1 but rather it comes from another framework called WebWork. There are still a few similarities around the MVC pattern (Action classes, etc.). The validation and configuration XML files change. Struts2 uses the Dojo toolkit for many of it's JavaScript functionality. IMHO Struts2 has more features and improvements over Struts1, although it's probably not so widely spread in use as Struts1 is, at least not yet...
