I recommend to watch the following 1-hour recorded session of the past Build 2014 Developer Conference to learn about Roslyn (a.k.a the “compiler as service”):
The Future of C#
The title is somewhat misleading, since the session is not so much about the future of C# (the language) but about the C# compiler, that is, Roslyn. It also covers VB.NET, by the way. In that session Dustin Campbell shows demos about using Roslyn to do powerful things with the code in a (apparently) very easy manner.
One cool thing (for developers of Visual Studio extensions) is that the Visual Studio IDE will use only the same public API that is offered to extensions. That should guarantee that no longer happens what is happening so far: while VS has access to the compiler, your add-in or package has to use the code model (EnvDTE.Project.CodeModel, EnvDTE.ProjectItem.FileCodeModel), which is much less powerful and much more buggy.
It also seems that Roslyn will be very well documented, and furthermore being open source you can examine it, rather than using reverse-engineering.