It's difficult to give Mao-chan a rating.
Each episode is only about 12 minutes long, and a chunk of each episode is taken up by stock footage of the girls' sparkly transformation into uniformed defenders.
Mao-chan has got a lot of characters, and something of a plotline, but what it's got the most of is almost unbearable cuteness. Think Chiyo-chan times three. The show has the hypnotic power of an episode of Teletubbies...you sit there staring at it, saying "I can't believe I'm actually watching this" but can't bring yourself to turn it off.
Each girl has her own pet assault vehicle. Mao, for example, rides in a tank, code named 'White Tiger' but renamed 'Mi-kun' by Mao. The tank looks totally like a tank, but is somehow oddly endowed with the glow of cuteness. The three competing grandfathers are cute. The alien spies are cute. The romance storyline between Mai's teacher and grandfather is cute. I haven't seen the leader of the aliens yet, but am willing to bet that if I watch enough of the series to see him, HE'LL be cute! Nobody's been disembowelled or decapitated in their battles, but if it happens, gosh darned if they won't find a way to make it cute!
So, if you want a series that will make you pound your heels into the carpet and squeal with the sheer KAWAIIINESS of it all, I present to you Mao-chan.
If you have a low tolerance for sparkly, spunky, sugary pixies...keep well away.