Communist Mutants From Space

This is the first game with bullet-time. How cool is that? (Actually that's a lie, Sega's Astro Blaster predates it.)

Commie Mutants is less political than it might seem; the title is purely decorative, and it's just a harmless Galaxian clone. It introduces some pretty great features like an incredibly extensive options menu screen where, other than selecting the number of players and difficulty, you can also put settings such as time-warp(which slows down all enemies and their bullets for a time period), shield, and strikethrough shots, enabling you to balance the playing field to your level. And I do recommend you do that, because the mothership keeps respawning the enemies by the second, and it's absolutely impossible to kill it in the later levels without the strikethrough bonus.