Descent
Parallax Software released Descent on a market saturated by me-too Doom clones (like Rise of the Triad, which was released in the same month) using that game’s cunningly coded 2.5D engine. Descent was having none of that – it was full 3D and this resulted in an initially steep learning curve. Once the learning was out of the way though, one could strafe in three dimensions.
Your initial craft was pathetically equipped and it soon became obvious that you would need more than firepower to get through each level. A certain sneakiness was the order of the day. Fleeing enemy bots, hiding in the shadows above a lava-filled pit, it was all good.

Later on came Gauss cannons, laser and plasma upgrades and the ubiquitous heat-seeking missiles. Of course, your enemies were similarly armed and as well as being able to dish it out, could dodge your incoming fire by ducking around corners and into lift-shafts.
Although the game had an auto-centre feature, with practice most realised that it didn’t really matter which way was up as you dived through doors, ducked under ledges and climbed steep shafts.
Your mission, was to rescue the trapped miners, trigger the mine’s core and escape before the blast got you, which made for some intense fleeing – the flickering lights and running dogfights only adding to the atmosphere.

Special mention must go to Descent’s mapping system. A wire-frame representation of the level, it was the most confusing and ultimately useless map I have ever seen. Indeed this may have been more than just my perception as true 3D shooters have largely abandoned 3D maps ever since.
Interplay & Parallax went on to produce Descent 2 and from there some of the original designers developed Descent Freespace but that’s another story.