I think it's mostly just supposed to be funny and cute. I think the satire that is in it is mostly making fun of the ridiculousness of many anime and how kids often get to wield incredible power, by taking it to the extreme and giving little girls state-of-the-art weapons of war and poorly-understood alien technology... which are also cute. The later episodes go into how this situation came about and then play with the characters and ideas. I think it has a worthwhile and original central idea too-- aliens that have a defense (whether it's intentional or not, I'm not sure) of being completely adorable, and fighting that with a force that's even more adorable to keep the public from sympathizing with the invaders.
If you like goofy comedy you should watch it.