Just a note to my future self and to anyone else who might stumble on this:
We created an MSI to install our MVC app, but the new test server refused to install it:
The Installer simply stopped, with an Installation interrupted message, and the application event log listed the following:
Windows Installer installed the product. Product Name: XXXXX. Product Version: x.y.z. Product Language: 1033. Installation success or error status: 1603.
The correct google search term here is: Installation success or error status: 1603.
It will lead you to the solution by Ben Noyce at NInitiative:
Long nights and story short, in order to install a web setup project on Windows Server 2008 and IIS 7, you need to install the IIS 6 Metabase Compatibility role service.