My first impression so far has been "Oh my Metro". I am not sure if I like it yet.
The menus are in all CAPS. WHY IS THE IDE YELLING AT ME?
The color scheme is a bit washed out. I am still trying to get used to this but it does telegraph to the code and designer as they are where your eyes go. I could get in to this high contrast look if it were to splash color at the portion of the UI I were currently using.
WPF Control / Element selection works well and very fast.
The UI is very responsive. If you remember Visual Studio 2008 (Ugh I still have to work in VS2008) clicking on a UI element in the designer renders properties in about a minute if you are lucky (and have ReSharper disabled). Visual Studio 2012's new IDE is very responsive. Thank you!
Visual Studio 2012 adds List as an option for your DataSources if you are a drag and drop binding kinda guy.
The XAML Designer has some Blend functionality built right in now. From the left: Zoom Level, Toggle Effects, Show Snap Grid, Snap to Grid Lines, Snap to Snaplines, Show Annotations.
This allows you to turn off the special effects bound to controls. This helps speed up the designer a great deal.
Allows you to view annotations about your WPF application (presumably from a sketchflow annotation).
The Solution Explorer looks Metrofied and adds a really useful Collapse All command and a Pending Changes filter command.