I've drawn from a lot of elements for the style of Penetrator from a variety of sources. Here’s a short list of shows and movies that inspired me, in alphabetical order:

The 310 to Yuma
Andromeda
Blade Runner
Cowboy Bebop
Die-Hard Movie Series
EVE-Online
Firefly/Serenity
Fullmetal Alchemist
Ghost in the Shell
Ghost in the Shell: Stand-Alone Complex
Johnny Mneumonic
Kenshin
Pitch Black
Shadowrun (3E/4E)
Cyberpunk 2077
Watch Dogs

Got around to creating an Imgur Album with some pictures from these sources. I found better pictures from some than others. Some are sources of inspiration for visual reasons, some for plot or character reasons, others for more esoteric reasons...but this album is pretty representative of the game I'd like to have, I think.