Descent

Descent, released in 1995 by Parallax Software, was one of the pioneers of fully three-dimensional action in enclosed spaces — the player flies a PTMC mining craft through a maze of tunnels at any orientation, with no fixed "up" or "down," a genuinely new and, for many players, initially disorienting experience at a time when shooters like Doom stayed flat. Six-degrees-of-freedom flight, combat against AI-controlled robots, and the need to navigate increasingly intricate mine-shaft mazes became the series' trademark.

The sequel, Descent II (1996), expanded the weapon roster, added new enemy types and more elaborate environments, and kept the same demands on spatial orientation; the series found a devoted following partly thanks to its unusual support for early headsets such as the VFX1, one of the first attempts at virtual reality in games. A PlayStation port brought the game to console players as well, even though 3D movement without gravity remained harder to manage on a gamepad than with keyboard and mouse. Later entries and expansions kept developing the arsenal and combat systems further without moving away from the core principle of flight in any direction.

Descent never reached the mainstream popularity of ground-based shooters, but among genre fans it earned a reputation as one of the most demanding and distinctive action games of the 1990s; its six-degrees-of-freedom flight went for a long time without a true successor, and a small circle of games inspired by so-called "six degrees of freedom" design still cite it today.