The series starts off great. There are around 5 excellently developed characters; there's a great premise; the plot develops logically and compellingly; the pacing of building tension then action is spot on. You've got a unique feel, and some moral dilemma action thought-provoking action. Everything has a balanced and cohesive feel - pretty much everything you'd expect when you see a series rated 8.9.

*I have to warn a very slight plot spoil, but I won't give anything remotely specific.*

Then about halfway through the series, to solve some stagnation they throw in a good dose of anticlimax. Now the majority of the interesting characters stop getting any screen time for various reasons and follow up by introducing and then disposing of characters you never have any reason to care about. The very ending was well done. (Pity it wouldn't make sense if you just skipped the 15 episodes preceding it!)

Maybe the manga developed all of the lame characters in the second half and had I first read all of them I would have enjoyed it all, but still... I just can't justify how sloppy everything got. Compare with either of the Fullmetal Alchemist adaptations, or Code Geass if you can tolerate mecha action, and you'll see where I'm coming from.

It either needed to be around 20-25 episodes and finish off strong without all of the later stuff, of have been extended to at least 50 so that they could have developed the last half into something workable.