I just set my system up and only checked the request filtering box in IIS. It installed a bunch of files and folders in the Windows\System32\inetsrv folder. I then unchecked the same box and it restarted and uninstalled all of those files.
I did not try to set a configuration on the install so there may have been no requirement that might have stopped me from doing a normal uninstall.
It is noteworthy that most of the IIS situations revolve around the isssetup.exe file which won't run normally. If your next upgrade attempt fails, all I could think is a .Net situation. But maybe when one problem is repaired, another one will show up..