From the arcade game of the same name, Galaxians is very like Space Invaders and the rules are virtually identical. The main difference is in the screen display. There are no shields for your laser base to hide under, and the invaders do not attempt to reach the ground and land.
Occasionally groups of aliens break off from the left or right flanks, flip over and swoop down, firing missiles at you as they go. In Artic's version this is the only time at which the aliens fire, but as time goes on more and more break off and it becomes very difficult to dodge them - let alone hit them.
This is a well-written version and the graphics are fast, although they tend to flicker slightly. The little aliens flip and swoop gracefuly. Ample in-structions are given at the start, though the game is really self explanatory.