IMO it started being a asspull from the moment Aizen showed he fused with the hougyukou. It all just went downhill, the explanation of the hougyukou true nature was stupid, OP and barely a explanation, every badass strong character couldnt do shit against him, they all got cut down (but none died, asspull), his single injury was recovered, but out of the blue Ichigo (who should be weak compared to most of those guys) got a huuuuge power up that enabled him to defeat god-like Aizen. Why couldnt the gotei put up a good fight, get beaten while doing some damaged, and then Ichigo with a minor power up finish the job, that would be more plausible. Although I have to admit that from an artistic POV It was pretty awsome