The storyline is this: In a pocket universe, a technologically advanced civilization has sprung up among different planets. A space traveler (a 'micronaut,' for these beings call their universe the Microverse) named Arcturus Rann was dispatched a millenium ago to telepathically (?) study various planets and alien races not yet encountered, while in suspended animation (his robot servant flew his ship). In the meantime, however, a faster means of travel was discovered, and a leading scientist named Baron Karza used his technologies to gain power. Although a military strongman, using his genetically-enhanced 'dog soldiers' to consolidate his power, Karza also has gained the loyalty of millions by giving them immortality - using his 'body banks' he takes the DNA of political enemies and restores the youth and vitality of those willing to submit to his rule. A strong militarized race called the Acroyear at first opposed him, until one of their royal family betrayed his people and now is part of Karza's armed forces.
Standing against Karza's rule is a small, motley band of heroes: Commander Rann, the micronaut; the enslaved princess, Marionette; a green-skinned member of the 'instectivorids' called simply Bug; a pair of mismatched robots, Biotron and Microtron; and the super-strong heir to the acroyear, who is called only Acroyear. The group, outnumbered, escapes to Earth in Rann's ship, the Endeavor - and are shocked to discover that here, they are the size of toys. Karza's troops give chase to our world, and the reports of tiny UFO's abound.
Besides the galactic-war plot, the conceit of having the Micronauts being the size of toys in our world is actually a really good idea - it let imaginative kids pretend that their own toys were actually warriors from another world, bent on freeing their home universe from tyranny, maybe with the kid's help. The Micronauts were a neat little line of action figures with interchangeable parts; the different body parts were human-like, animal-like, and robotic, so that a kid could come up with all kinds of neat combinations to form fabulous heroes or monstrous enemies. It all even fit within the storyline - Karza's DNA-altering body banks could create chimeras to bedevil the protagonists.
The series was very well-written in the beginning, less so as time wore on, but always fairly interesting; the art was not quite to my tastes (Michael Golden did the first several issues, later Howard Chaykin, Gil Kane, and others) but it served the story well enough. The series must have been fairly popular, however, because it lasted until 1984 - four years after the last series of Micronauts toys were released.
Come to think of it, the Rom comic did too. I wonder what this says about comic books, or about toys.
You can see a gallery of the Micronauts comic book here.