The classic Defenders (Atari 2600 and other platforms) but then in a first person 3D perspective.
This game is to be run with a 16K expansion module.
You fly over a planet and have a proximity radar indicating where (left-right) an enemy is. Your radar can show false hits when meteorites fall down.
The enemies go down and you get points (250) if you shoot them before they reach the ground. The enemies will shoot at you and you will have to try to prevent being hit. If an enemy reaches the ground and can fly up and away again you loose points (50). You have a shield which can take take 10 hits.
With either one of the keys q-t moves you left-down. y-p right-down. a-g left-up, h-newline right up. z-m shoots the laser. Using two keys at once allows you to move non-diagonal.
3D Monster Maze is a computer game developed from an idea by J.K.Greye and programmed by Malcolm Evans in 1981 for the Sinclair ZX81 platform with the 16 KB memory expansion. The game was initially released by J. K. Greye Software in early 1982 and re-released later the same year by Evans' own startup, New Generation Software. Rendered using low-resolution character block "graphics", it was one of the first 3D games for a home computer, and the first game incorporating typical elements of the genre that would later be termed survival horror.
3D Monster Maze puts the player in a maze with one exit and a hostile monster, the Tyrannosaurus rex. There, the player must traverse the maze, from the first-person perspective, and escape through the exit without being eaten.