"Go To Definition" in Visual Studio only brings up the Metadata

Well, another developer found the answer. The specific project we had an issue with was originally added as a file reference, then removed and added as a Project Reference. Visual Studio however, kept both in the csproj file for the web site, causing the issue. He went in and manually edited the csproj file to remove the file reference to the problem project and all is fixed now

It happens when you don't add reference as a project but point to a dll or exe using Browse tab in Add Reference dialog. If you add reference using Projects tab you should go directly to the source code when you select Go To Definition.

However, if you install ReSharper, you'll go to source code even if you added your reference to a dll/exe using Browse tab.