My MVC 4 App fails to load on Azure. How do I find out what is wrong?

My MVC 4 App fails to load on Azure. How do I find out what is wrong?

We have an app that we recently upgraded from MVC 3 to MVC 4 and from
Visual Studio 2010 to 2012. We're trying to deploy it to Azure, but it
doesn't seem to want to run there. It works locally, in IIS Express and
the Azure emulator. We can build the image just fine through Visual Studio
and via our msbuild project on the command line. We deploy just fine as
well.
Then when we browse to our deployment's URL, we get a 500 error, with the
message "There is a problem with the resource you are looking for, and it
cannot be displayed." It's not a YSOD, which leads me to believe the app
can't even start, but the message above is the only feedback I get.
We've tried a bunch of things to get it to work:
Upgraded to the latest Azure SDK
Changed the target framework on the app to .NET 4.5
Deployed on Windows Server 2012 instance
Nothing seems to help. If you know exactly what is wrong, please enlighten
me. But what would help immensely is to find the details on that 500 error
message I get when I browse. How can I get that?