I have an existing ASP.NET MVC 2 application that is working well and is usually easy to maintain. I had a lull in development yesterday so I upgraded the solution to ASP.NET MVC 3 and everything appears to be working.
I've been researching ASP.NET MVC 3 and there are a number of improvements including the Razor view engine, integrated support for unobtrusive JavaScript, etc.. These all seem interesting but not necessarily for an existing application that already has dumb views, unobtrusive JavaScript with jQuery, dependency injection, unit testing, etc..
What ASP.NET MVC 3 features, if any, could have the greatest impact on an existing MVC 2 application?