Developed and published by Team17, it was regarded as one of the best shooter games for that platform at the time, both for its technical excellence in graphics and sounds, and for its difficult and interesting gameplay. The game resembles Konami's side-scrolling shooter games such as Gradius, Salamander and Parodius.

In a classical scrolling shooter fashion, players control a spacecraft battling with hundreds of alien ships. Various power-ups, numerous in the first level but increasingly rare afterwards, permit an exponential increase of the spacecraft's seven different weapons (Guns, Buildup, Side shots, Homing missiles, Plasma, Magma, Laserbeam).

The game is composed of five levels. Many players never completed the second one (which had a very difficult ending), and most of the rest never went past level three. When Team17 realized this, they released Project-X SE, a special edition with the difficulty toned down. It was released as a budget game. A hack for the original game to enable the player to skip levels by holding down the fire button and pressing the escape key was also distributed on the coverdisks of several Amiga magazines.

It was followed by an equally difficult PlayStation-only sequel, titled X2. The game was also parodied in one level of Team 17's own Superfrog, as Project-F (with the F presumably standing for \"Frog\"), even going as far as using a remixed version of the original game's theme tune.