It's got a few really big problems that bring it down .
First the pacing of the story is abysmally slow for the first 13 episodes or so. Initially it just plods along it tries to be action oriented but fails and mostly spins its wheels with throw away plot elements. Admittedly it does get character development going, but it does so with what are mostly irrelevant story lines.
Second it really doesn't decide what it wants to be. Does it want to be a character driven shoujo, yuri kind of anime ? Does it want to be an action spy flick ? Does it want to be a slice of life ? It doesn't know, and it's trying for all the above.
Thirdly if you saw the OVA that this is the sequel to it fails to deliver on what you have been made to expect from that OVA. It eventually does deliver but by the time it does the series is nearly over.
TL:DR It does some things really well but because of the length of the series and its lack of focus it undermines its strong points.
