NOTE: This rant is talking about Aizen's stuff from the anime. I'm not reading the manga at the moment but from what I've heard, Aizen caused a whole mess of other overly complicated stuff in the manga that only serves to lower my opinion of him.
Let me just start by saying that I do not hate Bleach and I had no problem with Aizen until this arc. I'm just getting tired of the route Kubo is going with Aizen and how he keeps manipulating the rules of his universe to do some really stupid things. He tried to make this awesome, omnipotent villian but he did it in such a way that Aizen became too over the top and turned into an unbelievable villian. Aizen had a lot of potential to be a good villian but Kubo just went too far with him. Anyways, enough of that, its time to get down to business.
1. The Plan: Now where do I begin with Aizen? Lets start with how the anime pretty much admits that he was behind everything in the series up until now. He seemingly manipulated hundreds of years of events. He even butchered the Soul Society's government to make sure his plans went off without a hitch yet left the one person who could supposedly match his intelligence (Urahara) alive. Why not kill Urahara once he found Rukia so no one outside the Soul Society can stop him? You could argue that its his pride that keeps him from doing so and that he thinks he is smarter than Urahara, but to me thats just a cop out. To top it all off, his entire plan relied on Ichigo not letting Rukia die in the first episode, gaining Soul Reaper powers, losing his soul reaper powers only to get his soul reaper powers back along with hollow powers and not dying in the process, gaining Bankai, and not dying until this point. I take it back...Aizen isn't a genius, he is the luckiest villain I've ever seen. This kind of plan is by far one of the dumbest plot devices in existance because it relies on too many variables in order for it to work and it is the absolute worst way of getting a villain's intelligence across. It essentially equates to the writer saying "How do I make my new villian look like a genius? Oh I know, I'll make him the source of the entire plot and have him manipulate the hero to get to this point. They'll never see that coming!". Kubo pretty much expects us to believe that Aizen somehow foresaw hundreds of years of events. I can understand using this sort of thing for a short (1-13 episodes) or medium-length (13-26 and sometimes 50 episodes) anime, but doing this reveal after more than 200 episodes is absolutely stupid (yes I know that happened because the manga was so long and due to a lot of filler in the anime) and only re-enforces how unlikely this plan is to succeed as well as how lucky the villain is that it actually worked.
Seriously, I know its just a tv show and its supposed to have some degree of predictability and of course Ichigo was going to do all of that anyway, but for Aizen not to have any other alternative in case something screwed up is just stupid. He totally jumps the shark during this arc and pretty much "God Modes" all of his fights, meaning no matter what the heroes do he will most likely have an answer for it just because the plot says so. The Hogyoku only serves to make him worse (but thats another part of the rant entirely). The power imbalance between Aizen and the heroes is just ridiculous.
2. His Logic And Wasted Effort: Further more, I have to outright question his need to create the Espada with the Hogyoku for the sole purpose of being nothing but cannon fodder. He has admitted that he is at least 5 times stronger than most of the captains and even twice as strong as Ichigo hollowfied, so what was the point in doing that? Why did Aizen waste so much time and effort creating cannon fodder when he could have obliterated the Soul Society after gaining the Hogyoku and then create the Ohken (Royal Key)? Normally I admire strategic villains but Aizen is just too much and wastes so much effort for something that should be a simple feat for someone like him. Though I have to admit, I must give him credit for developing Wonderwiess the way he did. That was a stroke of brilliance on his part.
3. The Zanpakuto: Now for possibly the most broken thing about him and what leads to his inconsistent abilities, his zanpakuto Kyoka Suigetsu. It is just stupidly powerful. It can manipulate the five senses to make his opponents see, feel, hear, taste, or smell whatever Aizen wants them to. Anyone who sees the sword's released form is essentially under his control and he can regain control by releasing the sword again, with Ichigo being the only one who has a chance against him because he has never seen it before. I bring this up now because at one point Aizen tricks the Soul Reapers into thinking they are fighting him and when "he" gets impaled by Toshiro he reveals that it was Momo with Aizen disguised as Momo getting healed by Izuru, which makes the audience think that Momo was the Aizen they were fighting this entire time. I call BS on this because not once during the fight did Aizen ever release his zanpakuto. Furthermore Ichigo was fighting that Aizen at the beginning of the episode so why did he fall for it when he is supposed to be immune? The Momo Aizen even managed to wound the captains fighting him/her before the illusion was broken so how did those wounds still remain after the reveal? And how did Tosen die from the illusion Aizen's sword going through his skull? Illusions do not work like that. Furthermore, regardless of how convincing the illusion was, its still an illusion which makes the wounds remaining far more puzzling when you consider two more things: 1. Momo, no matter how good she may be, cannot fight on Aizen's level so she likely wouldn't be able to damage the captains. 2. Momo was supposedly unconcious for the last 10 episodes meaning it was the illusion that dealt the damage. His zanpakuto can only make you think the illusion is real, make you feel the pain from the illusion cutting you, and make you see a wound that isn't there. It does not make the victim's or the wielder's thoughts a reality!! No matter how convinced they are that they have been injured, the wounds should still vanish after the illusion was broken. As for how he used his zanpakuto's powers without releasing it, I suppose you could argue that Aizen's zanpakuto is like Ichigo's with it being a constant release zanpakuto (which contradicts what happened earlier in the series as he released it in the normal manner), but then that creates a plot-hole as Ichigo would've technically seen the released form during this fight (due to the captains telling him to keep his eyes on Aizen while they tried to make an opening for him to strike) which would mean he isn't immune anymore. So yeah, either Ichigo isn't immune or Kubo pulled some major BS with this reveal! I've heard some people say that all of this was explained in a panel of the manga but that was never shown in the anime.
4. The Broken Rule and The Last Straw: For Kubo to throw out one of the most basic rules for his show is just stupid, that rule being that in order for a zanpakuto's power to be released the soul reaper must say the release command for their sword as well as the sword's name (with Ichigo's being an exception since it is locked in shikai, Aizen however has no excuse as he was shown releasing it in the normal manner earlier in the series). It looks like Kubo only removed that restriction for Aizen simply to show how broken he is. It doesn't help that Aizen just had to use Momo for the decoy. What makes it more frustrating is that I would've been fine knowing that the Aizen they were fighting was just an illusion, I seriously could've accepted that revelation, but no...oh no, Kubo just HAD to have Momo be the one used as the decoy. Seriously why Momo? She is a character that hasn't done much thus far in the anime except get seriously hurt and her only notable role so far is that she is Toshiro's childhood friend. She does not deserve that. I absolutely hate it when writers do that just for shock value. Kubo seems to like using her for Aizen's punching bag or having her gravely wounded just to anger Toshiro. Whats worse is that nothing usually comes from it. Toshiro just gets mad only to have Aizen kick him around or take him out with one blow immediately afterwards.
I would've been fine knowing that entire fight was an illusion, but to throw Momo into it just to anger Toshiro is unacceptable. It serves no purpose other than to re-enforce that Aizen is a jerk, which is something anyone who has followed the anime already knows. What was the point in even using her for that?!! Momo being the decoy is the thing that pushed me over the edge and what made me decide to reflect back on everything I hate about Aizen for this rant.
You also don't get much of a feeling of Aizen being tough other than how the show exposites about his percieved strength, how the show says he caused everything in the show, and plot-convience that makes it happen. I'm going to draw a comparison to another anime that does the powerful villain idea better than Bleach: That anime would be Naruto. Naruto does villains like this so much better and doesn't bend the rules of its universe too much for villains. In Naruto, the villains actually show how strong they are instead of people just talking about how strong a villain is. Take Orochimaru's attack on the Hidden Leaf Village for example, the heroes were not shown to be outright incompetent and you have the Third Hokage admit that he probably won't survive this fight and he tries to take Orochimaru down with him and once he realizes that he can't, he does his best to disable Orochimaru for a while. Even Zabuza's arc showed that he wasn't all talk and could actually back up the characters' exposition without needing plot-convience to make it happen. Even in The Fourth Great Ninja war, the side characters don't just get walked all over by the villains. You shouldn't try to show that a villian is strong by making him able to overpower his opponents so easily.
5. The God Sphere: Now for the Hogyoku, oh I can't tell you how much I hate this thing right now.
Due to its abilities I have decided to call it the God Sphere (because that's essentially what it makes Aizen). It had potential, but its use has begun to aggravate me. Aizen fuses with it and it essentially gives him the ability to "evolve" into stronger forms (as well as faster healing abilities as shown when Ichigo cut him right before he revealed that he had fused with it). It also effectively puts him even further into god mode. I'd honestly be more shocked at how much stronger it made him if he had actually fought for an extended period before this arc. It makes it extremely hard to tell how much his power increases because every fight he has had before this arc has been a blowout with him either fighting soul reapers one-on-one and blowing them away with one swing or outright dominating all of the captains in a fight with Kyoka Suigetsu. We have nothing to compare his physical fighting power to until after he has already fused with the stupid thing and seemingly gained more power. The guy is basically able to juggle Yoruichi, Kisuke, and Isshin at once after the "evolution". All of whom have power that is above that of a captain class soul reaper. Why not at least show him struggling against them before forcing the evolution? Seriously, as soon as Kisuke shows up, Aizen evolves. You kill the suspense when you do that. When you raise a villain's power level like that without showing what he could do before the increase, it makes it look like you're just trying to create a god-like villain. His evolutions also pretty much grant him the death-touch for people with little to no spiritual pressure.
This next power is likely the most ridiculous thing I've seen in this arc: If the Hogyoku gets removed from his body, he can regenerate around the thing and it apparently forces another evolution. Normally, I wouldn't mind something like that if the Hogyoku's powers were spread around to multiple characters with each character only receiving one power from it, but its all being given to just one guy who was already insanely powerful thanks to Kyoka Suigetsu and its all done just to keep him important to the plot. It even makes him immortal even after it gets destroyed. Even without the stupid God Sphere, he can no longer be killed!! All that combined with his zanpakuto is just ridiculous! At this point, my suspension of disbelief is officially gone and I can no longer take Aizen seriously as a villain. Aizen could've been so much more interesting if they made him either insanely smart or insanely strong not both. He had potential but the route Kubo took him was just stupid. They didn't have to make him god-like. Since the Karakura arc is now over and Aizen is now defeated, I'll try not to let this color my perception of the anime's final seasons but at this point, my suspension of disbelief is gone and its going to take a while before I get it back for Bleach.