Generally bug fixes and performance enhancements.
One cool addition for me, is the HTML input helpers supporting array/collection indexes, for example: Html.EditorFor(foo=>foo.bar[i]) . I was working around this limitation using Html.EditorFor((foo)=>foo.bar[i], “Bar”) i.e. passing a function expression, but this means you have to pass a template name (to get the correct HtmlFieldPrefix), this addition means cleaner code and no hard references to templates, thanks MVC team.
Another notable change is Query 1.4.1, is now included by default with ASP.NET MVC 2 projects.
More info @ScottGu’s blog: http://weblogs.asp.net/scottgu/archive/2010/02/05/asp-net-mvc-2-release-candidate-2-now-available.aspx