Cabewse 
About Aizen's Bankai.
Very simple really. Once you've laid your eyes on it, Aizen can make you believe whatever he wants you to believe. It fools all five senses.
So Aizens shows almost everyone, Captains included, his shikai before. Once they've seen the shikai, all Aizen needs to do is show the sword and EVERYONE who SEES the sword is trapped in an illusion.
Think of Uchiha Itachi's Mangekyo Sharingan. Once he looks into your eye with that technique, you are trapped in his realm where he controls the universe and surroundings. Same principle as Aizen's Shikai except that the Shikai doesn't really alter your surroundings, it merely makes you see whatever Aizen wants you to believe.
By the way, does it occur to anyone how odd that Aizen and Gin left Captain Unohana alone whereas Aizen killed Hitsugaya off? Does this mean that Unohana is actually much much stronger than Aizen? I mean, there's only Unohana and her Vice Captain of the 4th Squad, the so called weakest squad of the Gotei 13 and Aizen RUNS from Unohana after baring the whole truth to her.
Me thinks Aizen is afraid of Unohana taichou. Guess it would makes sense since doctors would be the most deadly killers.
Despite me hating Hinamori, it was a stab to the heart (for Hinamori literally) to see her get skewered by her greatest role model. And that bloody Aizen was smiling all the way. Poxy son of a whore. However bimboish she was, nobody deserves to be btrayed like that.
Curse Aizen, Gin and that stuck-up Tosen as well. You know, the animators really did Aizen's face well. From the point Aizen stabbed Hinamori, his eyes just look.... empty. Devoid of emotion. His smile is so empty, its creepy. Its not the mad scientist look, its just.... something else. If I were to describe it, I would say... TRUE EVIL. Its like this guy in Babylon 5, Mr. Morden who always smiles but brings death and destruction to the galaxy.
Somehow I doubt Ichigo can defeat Aizen. He barely got through Byakuya and can anyone think of a way of countering Aizen's shikai?
Actually, all you need is to blind yourself, which is something Ichigo has not trained himself to do. If you can't see the Shikai, it won't work on you. That's why it doesn't work on Tosen and Tosen is acting on his own free will.
