The premise of a darker and more shady story with so much death in it in the same universe as a usually pretty light series in the main story of index was a great concept. I loved the art style change at the end there to put emphasis on how brutal what was going on actually was. They kept Accelerators personality dedicated to the way he was. The ost was great. The only gripe I would have with it would be the lack of character development in the title character. But I guess the development of Ester was done well too.