The plot really focuses on the relationship between Nadie and Ellis, the two main characters, and also, on Ellis's past and background. There's a lot of character development, and a very strongly coherent plot which has plenty of twists and turns to keep you riveted to your seat.
There's not a lot of fan service, which is probably a good thing since this was intended to be a semi-realistic series, with a serious plot. There's as much action as there is character development, so this is far from being a melodrama anime, and also adds a hint of mystery, as you explore the background of the two main characters (mainly Ellis).
The series ties up all it's odds and ends, and like some shows, does not leave you with a cliff hangar. The ending is IMO very satisfying, and altogether I give this show 5 stars!