This should be on my list, but isn't. . .
Programs that feature an Un-Install that leaves stuff behind.
When I test a program that I must install, I also try to UN-INSTALL it as well. Too often, pieces get left behind.
I can forgive a configuration file in my %AppData% folder that gets created when I run the program, but when the package's folder in %ProgramFiles% (including all the files in it) gets overlooked, there's no excuse!
Too bad people who write reviews rarely test this. It's kinda important to know that if one installs a program that they'll have a Devil of a time getting rid of it if they change their mind.
Cheers, PW.