Postal Short
Released in 1997. Postal was a massively controversial game in a year where Carmageddon and the first Grand Theft Auto were released. The controversy mostly centred around title and it's links to US post office shootings.
I don't know if the creators meant to offend with the name but they certainly meant to shock with the imagery. The menu and cutscenes all show twisted artwork of skeletons, monsters and malformed bodies. The game itself isn't quite as shocking by todays standards. Games where you go out to kill people are pretty common but they tend to have a bit more to them in the form of side missions or a full story. Still the spiritual successor Hatred was released with a decent reception in 2014, so the just go out and kill things sales pitch does work.
It's 4 hour playtime is just enough to keep it entertaining throughout. The settings are varied and can invoked a feeling of unease as you go through some areas while other victims are almost deserving of their fate.
The game is available from