In Bleach, Aizen had an incredibly complicated plan that seemed to span decades and that involved a lot of people he had no control over doing what he wanted them to do? I found it pretty difficult to follow what was going on in terms of what exactly his plan was. Can someone summarize it for me?
Aizen wanted to create the Ouken, the key that opens the door to the Soul King who rules Soul Society. In order to be able to keep increasing his power he wanted to merge the powers of Hollows and Soul Reapers, this was his experiment with the Visoreds. Aizen had made his own version of the Hogyoku to do this but it was incomplete, he merged it with the one Urahara made and with that he had the finished one that allowed him to increase his power and become the ultimate being. Aizen said himself that only Urahara was the only intellectual challenge he might have had.
Remember though that Aizen had his hypnotic power that allowed him to control many of those within Soul Society, those he did not control he tricked. He was able to get many to do his bidding, knowingly or not, only Ichigo was not under his control since he had never seen the sword release.
Ichigo made a statement after killing Aizen that Aizen was so powerful that having no equal he felt there was no one to challenge him and was somewhat lonely; the part about crossing swords where all Ichigo felt was lonliness. It's possible to look at this as the only one who could be a challenge to Aizen was the Soul King, so creating the Ouken using Karkura Town would allow him to open the gateway to where the Soul King lived and possibly fight him and find an equal.