The story in short centers around an underwater (at 2500m down) base called Substation, taken over by aliens. You have to enter the game as a marine and investigate what has happened down there. The game took gameplay to another level on the STE with this in all areas. It was the first FPS ever developed for the STE platform, and was awesome because of that (a Wolfenstein 3D clone). It also featured multiplayer gaming using the MIDI port of the Atari computers.
The graphics were a breakthrough at the time for the enhanced ST platform. The game graphics offer a real-time rendered 3D environment, with 25 frames per second (!) at a small though resolution of 320x160. The graphics engine has no texture-mapping but instead uses Gourand-shading for the walls with mixture of bitmapped graphics for other game features in 16 screen colors in total. Note that the game was enhanced for the Atari Falcon 030 series with 256 colors on screen.
The sound offers a unique DD Audio (Distance and Direction) technique. If you have stereo speakers fitted to your STE (or Falcon), you will be able to determine the distance and direction of any in-game sounds! Also the game (via the STE enhanced sound chip) offers a variety of digitized SFX such as screams, footsteps, gunfire, engines, ventilation fans, emergency horns and others, running is three separate sound channels! Also a nice digitized music score at the intro and the menus is found.