The first two episodes were far better than I expected. Mecha were secondary to a complex plot, with several political layers and hints of an interesting main character. Though the tension and quality is not always at the same level, the first arc is a smart action seinen at its best.
Starting with the second arc at episode 14, the MC Kirico becomes more of a war machine than a human. He's still supposed to have strong feelings, but he hardly speaks and his acts are increasingly antisocial. Later on, the other characters loose even more depth than him. The main woman is moved around like a bagage that cries "Kirico" whenever some danger appears. The last arc was also disappointing since I hate sci-fi that turns to ex-machina god-like elements.
Overall, I still recommend it for an excellent start, for a few compelling episodes here and there, and because it obviously influenced many anime, e.g. Seikai no Monshou.