Maybe the nostalgia of this anime clouds me, but the 2.8 average it has as I'm writing this review seems really low. Three preciously cute girls in a monster-of-the-week showdown with cute aliens that only they can defeat (and by defeat, I mean non-violently transport away from Japan) are the only hope Japan has in facing the onslaught of very cute, but kind of destructive monsters. The manga was written by Ken Akamatsu, the writer of Love Hina, and there's a lot of LH references that make it to the anime, as well as just a healthy amount of humor and poking fun at itself.
This is a prime example demonstrating that entertaining does not need to mean complex and sophisticated. This series is as simplistic as a moe comedy can possibly get, and yet enjoyable to the max. The entirety of the underlying story can be summarized as "The Japanese defense forces decide to enlist three cute elementary school girls to fight against alien invaders in order to avoid accusations of bullying. Because the aliens are similarly supercute." The whole thing can be considered a parody (or a satire even) and revolves around just one gag but the way it is executed is what makes it a joy to watch. It is a silly little show but it plays out like some sort of military action thriller which makes the whole thing seem absurd in a hilarious way. The decision to have the entire BGM soundtrack be in the form of solo piano pieces was utter genius, adding much dramatism to contrast with the silliness taking place on screen. Each of our three heroines has her own charm though I personally find Sylvia the funniest of them all. It's simply impossible not to love that adorable airhead. The visuals are nothing to write home about but that really doesn't matter for a comedy show like this. Verdict: just watch it already!