I started watching this one from the day it aired.
I got to about episode 14 before my computer busted and after I got a new one I jumped into FFXI and ignored this for quite a few months.
At any rate coming back to it, it didn't seem to grapple me as much as it did when I started watching it. Seemed like it was supposed to run for 12 episodes, not more, and that they enhanced it much like Mai Hime because it recieved some popularity.
I still think that was true to a point, the main antagonist really didn't quite work out in the transition between the predicted story and the extended one. In the predicted story he was nice and calm as a pussy because he was just one of the extra characters, and then after episode twelve it was "MU-HA-HA I am evil. Note my smile. I smile because I am EVIL!", and after about episode 18 I thought "Well this isn't going anywhere, I'll probably stop after the next one".
Then I got to episode 19 where the final arc started. Turns out the three marginally boring episodes were there because they were setting the stage to rock your face off with some Dark City awesome storyline elements.
So full review - setting and story were pretty good at the start, sort of slow in the middle and then AWESOME in the end. They actually kept elements from episode one hidden until the very last episode where it all falls into place and you get a sense of "Wow, nice one there writer-dono".
Character development suffered a touch due to the fact they didn't know what to do exactly with it I guess, but all the same it worked out more or less allright. Can't really begrudge them for it considering they were probably aiming at an end at the 12th or 13th episode.
Animation's pretty good, music I guess as well, but the two of its most selling points are really above, the setting and the story.
Highly reccomended just for the resolving parts of the plot in the end.