MATRIX from Salamander is the second in Jeff Minter's Grid Wars series, and is based on the arcade classic Centipede. The centipedes move along a grid, which is gathering solar energy for Earth, and as well as attempting to collide with your spaceship they may also drop bombs on you.
At later levels the droids are aided by deflector shields which send your laser fire scattering in all directions except the one at which you aimed, and the now notorious cosmic cameloids, whose presence on the screen decreases your score until you have eliminated them.
Spectrum owners accustomed to the complex graphics and vast playing areas may feel dismissive about the Minter style. He writes simple games which are challenging and appeal particularly to zapper addicts.
The real strength of Matrix is its sheer speed of operation and the delicate game balance, which seems pitched at just the proper level to convince you that you could easily improve your high score if only you had another attempt. That is one of the core secrets of an addictive game.