This features includes:
ASP.NET AJAX - New functionality includes CSS selector APIs, navigation history support (Back button support), and more.
Silverlight Controls for ASP.NET - Enables the ability to integrate rich interactive application scenarios and add media (video, audio), vector graphics, and animations with new, powerful ASP.NET server controls – XAML and Media sever control.
Dynamic Data Controls for ASP.NET - Introduces a set of data controls that provide a simple, intuitive user interface for data-driven Web pages.
ASP.NET Application Services - Offers new application services to make AJAX and Silverlight Web applications more discoverable from search engines and easily searchable from within the site. Additional services help you gather and analyze data about client errors.
Dynamic Languages support in ASP.NET - Provides support for both IronPython and Managed Jscript, as well as the DLR (Dynamic Language Runtime) - extending the language choice for developers and brings the benefits of dynamic languages to the entire .NET platform from client to server. With the DLR you can use those same languages on the Server for ASP.NET Web applications, Web Services, and more.
To read more go to Microsoft site.