Windows Installer was / is a superb Micrsoft product. Sadly, not enough people understood the modular nature of the technology and its potentil was never properly realised.
SCCM is again pushing a modular software concept onto IT. Understanding what Windows Installer actually is about is critical for succesfully managing software in modern technical environments. I spent many years working in the area of Application Packaging, Application Management and deployment. I used the following pages of documentation as training material for young techs over the past decade. Some of the examples are a little dated but still relevant.
Feel free to amend and distribute any of the contents. :)