User blog comment:GinIchimaru/Why Aizen is not "Over-Powered"/@comment-1393830-20100409011155

Aizen is considered OP due to his Zanpakuto. It is has a simple but devastating effect. It is not op though because of its major flaw. You need to see the release in order for it to have an effect on you. Ichigo has yet to see it so Aizen cannot control his five senses. Aizen can take on all the captains because he changes what they are seeing. Yama was able to overcome this due to being stabbed by Aizen showing another weakness in his blade. Overall Aizen will always be considered op but if you carefully examine him, he is not