Whenever people are talking about Aika, the first things I get to hear are complains about panty shots, wannabe porn, wannabe hentai etc. Well, I guess for the vast majority of viewers, Aika is indeed nothing more than this.
However, a few will like the show, but for others things: The story is absurd, but funny and fast paced (I emphasize this because all the other Animes I've been watching so far seemed quite boring after some time). The characters are rather likable, except for Hagen and his sister, nobody is completely unappealing. There's a lot of violence in the show, but almost nobody gets killed and even seriously hurt (I really appreciate this in a action movie). Most of the characters are rather beautyful and some even admirable.
But the main reason for me to love Aika is the fact, that some of the characters even develop some deeper kind of identity. I mean, it is obvious that the creators didn't intend to make more than a simple action flick with only two dimensional characters. But nevertheless some of the characters seem to grow when the show is going on, and some of them I really learned to love (especially the White Delmo couple and the Golden Delmos).
In my opinion, the second series ("New mission", trial 5 to 7) is far better than the first, because it's less harsh but more entertaining (with these terrible Hagen and Nena being replaced by the much more appealing Miss Bianca and her crew).
Whether you enjoy the show or not, it's quite a matter of taste. However, there's more than just panties in it.