This series is definitely unique, I don't think I've ever seen anything like it, I did enjoy it though. It was hard to follow in some places, confusing in others, and just freaking weird all around.
The series revolves around Rin Asogi, a immortal P.I. who keeps getting tangled up in a supernatural conspiracy that involves her more than she knows.
There is a lot of weird twists and turns in the story that honestly keep you confused, even after the end. After watching it once, I suggest you watch it a second time, just to get a better understanding. The thing I like most about this series though is that it jumps right into this "world" and doesn't waste time with character development or how everything works, it just lets you figure it out on your own.
I read somewhere that it is a "Tech-Noir" series, I don't know exactly what that means but what I think it means is that even though it's not in the 40's-50's it still holds a Film Noir mood and it does feel like an old mystery movie.
Throughout the whole series there is intense female nudity and graphic bondage, and rape that isn't put in subtly, but it all ties into the plot so it's not just put in there for fun.
Finally, I add that you will either love this series or get so confused you don't like it. But I suggest you watch it, cause it is shockingly original and it's pretty awesome in it's own way.