In the mid 90's, even before the inception of id Software's QUAKE, there was Descent, a fully 3D first person shooter.
Descent, however wasn't a traditional game in it's genre, in most FPS you'd walk and shoot a few baddies,
not blow them up in pure six deegres of freedom. Not content with just breaking the mold, Descent also had fantastic AI and level design.
Descent II further expanded the ideas of it's predecessor, refining many of it's aspects.
Sadly Parallax Software, the original developers, became Volition and never produced a real sequel to their classic game.
That is until some of them decided to change that.
Overload is here, Descent II true's sucessor. A successful kickstarter brought the original team back together,
and with it, Revival Software's magnum opus.

You can get the game DRM-free here.