If you're a real fan of mecha/sci-fi/military-minded anime, I suggest going ahead and skipping Infinite Stratos. I think it'd be an utter slap to the face if you are one. Foremost, I think it would be classified as a harem. And then school-life/comedy, romance/ecchi. It just has some elements of mecha/sci-fi to set it off from others in its genre.