When editing Razor views, Visual Studio doesn't realize we're working with MVC, since we're in a desktop application. So it's not picking up any of the MVC assemblies, imports, etc.
It works fine once you compile and run, it's only an issue within the editor itself.
It would be great to figure out how to make Visual Studio handle these files correctly. Until then we have limited syntax highlighting, lots of erroneous errors, and no code completion to speak of.
Maybe a Visual Studio extension?