http://koti.mbnet.fi/ktalo/kapseli/pelit/2006--1/probotector/probokuvat.html
I think it's fascinating the extent they went to, because they didn't want to show "violence agaisnt humans". Instead, every enemy in the game is a robot, and you yourself are a robot.
And I absolutely love the box art

Probotector 1:

Probotector 3:

Probotector Gameboy(that's lame, it's the same as the NES..):

Probotector Megadrive (Contra: Hard Corps. My fave box art):

Thoughts? Personally, I just love it cause it's such extreme change, and the box art is so cool.