So after my last blog got so much traffic I decided I would make another one since the topic was drifting this way.
With Isshin showing up like he did, I think it is very safe to assume a few things. 1) He knew Aizen beforehand. With the casual way he showed up saying that Aizen talks too much and the big smile on his face, I think it is safe to assume those two knew each other in the past. 2)Isshin is very powerful, we know he has captain level power but I think it goes way beyond that. He showed up to fight one of the strongest shinigami of all time with a big smile on his face knowing full well how powerful his opponent is.
With these I have come up with a bit of a theory. I believe that Isshin is extremely powerful. More so than Ichigo. Aizen knew Isshin in the past and may have been envious of his power. When Isshin went to the real world for whatever reason, Aizen kept his eyes on him. When Isshin had a son, my belief is that Aizen came up with a plan to use his son to gain more power. Therefore I think I can take back a little of my last post and say that Aizen does not have esp. I find it very possible with his intellect, patience and manipulative ability that he could have sent Rukia to Karakura town where he then sent a hollow. We know he has had control over hollows for a long time so it is not odd that he could have sent one right to Ichigo's home. We know he had been following Ichigo since birth so it would not be hard to pinpoint where the hollow should be sent. He could have also had manipulated squad 6 into going to retrieve Rukia. From there it is not hard to imagine that he could have tipped off Zaraki to a strong opponent. I think in the coming chapters we will see a lot of this cleared up and while I don't know if I am right about all of this, I think at the very least Isshin's arrival has left the door open for many things.