Installer.SetInternalUI(InstallUIOptions.Full);
Installer.InstallProduct("example.msi", "ACTION=INSTALL");
starts Windows Installer all right, but in Classic look and feel. The .msi itself looks all right when started standalone (it uses WiX's own provided UI). How could it be forced to start looking nice?
Screenshot:
"Classic look" isn't a Windows Installer term and I've never heard it used in relation to installers. I'm not sure what exactly you are trying to do and what your install looks like after this dialog but I would like to call out that you can logically OR InstallUIOptions arguments to get a combination such as Reduced UI and Hide Cancel ( this would be equiv to msiexec ... /qb! )