I intend on this being a completely spoiler free review. Girly Air Force is about the definition of mediocre. If it was to be personified, it would be the guy in the room no one remembers because he is so incredibly average.
The art is nicely done, and CG isn't obtrusively done like so many other action anime. That alone gains it points in my book.
The audio was nicely done, but not so much the music. The music only seemed to really hit a high note (forgive the pun) one time for me... and it was in episode 12. This anime will not leave you humming any music from its intro, closing, battles, etc... it's just musically underwhelming.
The characters were pretty flimsy here as well, though I admit they were stronger than I'd have expected from something named "Girly Air Force"... so I guess that's a win?
Now the story was SUPER slow. And feels like it should have been a 24 episode season, that they cut in half. And all we got was the slow mood setting half of a season. The final episode is OBVIOUS it is now supposed to finally be entering the interesting story arc. Then... it ends. You get one episode of actually fairly fun enjoyable story, then you have to wait for what MIGHT be season 2 (or might never occur).
Anyway, TL:DR... mediocre, even by young girls personifying war machines standards. And it ends the moment it finally gets interesting.