Classic Game “Marathon” Free on Steam
Released in 1994, this game could be called a Doom clone. It used a game engine that couldn’t handle ramps, curves, or solid enemy models. You can’t even jump! But it still had great graphics and an entire short sci-fi novel hidden in terminals that gave you objectives and the plot. I played this *so* much and even helped with creating a makeover mod for it!
Available free on Steam.