I started watching and reading bleach the same year it released. Let me introduce you first hand to the suffering of many bleach fans such as myself after this ordeal of 15 years.
Are you having a bad day by any chance? Or a bad week or even a month? Whatever it is, be thankful that you are at least not Tite Kubo, who essentially retconned his entire career worth of creative work down the shitter, for seemingly no good reason. Let's begin!
What made bleach popular:
This might be outdated 15 years later, so if you start bleach today none of it might even hold true anymore because manga/anime has changed so much since then. Bleach in its own time was revolutionary. From the style of character designs, to the concept of soul society, to the distinctly emotionally intelligent/melancholic way the characters expressed themselves, to a huge line up of characters with amazing powers and untapped potential, bleach had it all. And boy did it deliver! Bleach's soul society arc is one of the best (maybe even the best) battle manga I came across in my time at least. The fight scenes were amazing, the characters were unique, the momentum of story telling was explosive. Could you ask for more in shounen? You couldn't, but Kubo delivered even more! The complex relationship dynamics between the characters, be it Rukia and Ichigo, or Byakuya and Renji or Rukia and Byakuya or Soifon and Yoruichi (SPECIALLY these two, because yuri hints in shounen in those times were an anomaly), it was these dynamics that made readers invested in the series like no other shounen. Readers wanted to know if Ichigo can master an attack, but more than that they also wanted to know what is he feeling in his heart. Even the relationship between Ichigo and the soul of his zanpaktou is very dramatic and full of mysteries.
What led to the slowdown:
Now comes the period when soul society arc is over. Kubo has pretty exhausted all the awesome plot devices and character designs he started out with and needs to come up with a new story. In the meantime he still had bonus material to work with like Ichigo's hollow transformation. The real issue begins with Hueco mundo arc, from completely unoriginal plot to long dragged out fights, to gazillions of unfleshed characters with same faces/personalities to seemingly non stop ass pull winning moves, the dominoes started to crumble one after the other. The exhaustion of not being able to write compelling scenes or develop the characters was clearly apparent in Kubo's writing. He would still pull his magic here and there but we could see a genuine decline in the story as well as a drop in quality of drawing.
What utterly destroyed bleach:
I don't know why, in a shounen to boot, Kubo came up with a plot device for hero to lose everything to make bad guy stop once (not even kill him, just restrain him) but I think that was the definite moment bleach tanked fully because there was no saving it from this deadend. Now in order to make bleach progress in any way, Ichigo needed his powers back, so Kubo had to come up with an entire asspull arc to provide a premise for Rukia to give Ichigo powers for a second time. The entire arc focused more on development of Rukia and Ichigo's relationship, isolating Ichigo from all other characters except Rukia, than it did on creating any meaningful plot that justified the existence of the full bringers in first place. Anyway, we can understand. Kubo did a major oopsie with the end of HM arc and needed something to fix it. And Ichigo needed some mature/romantic development. Gotcha! So now bleach is on track! And what does Kubo do in next arc? Utterly destroy and retcon every single character of the manga including the MC. It's not even a shounen at this point, it's a tragedy. If he had known any better, he would have stopped bleach at HM arc. If he didn't want to completely throw bleach into dustbin he would have at least stopped at fullbring arc. But making of the last arc required him to undo essentially the entirety to bleach and play with the bonds characters share with their fans, because he had no other ideas to create "wow factor" at this point to stir the pot. Bleach was already failing for years at this point and a large fraction of readers were passive or had zoned out completely. So here goes - What's that? An established villain? Let's make him good guy and save the hero. A dead person? Revive him. Revive ten of them actually then kill and revive them again. Let's create an utterly useless sidekick fight for 10 chapters and finish the series in one chapter which doesn't connect to anything that happened in the 699 chapters before. NOTHING in the last arc makes sense. The ending chapter is so OOC you might as well insert a fanfic there and it won't a difference, because there was no prelude whatsoever leading to the blank period, in fact the final boss battle ended mid fight with no conclusion. If you were reading a physical manga, you would think someone ripped a few pages off the chapter because it ends that abruptly. What's worse, by the end of the series, every character and plot development regressed back to zero, essentially making the whole point of the manga NADA ZILCH ZERO. If you were to ask today why did Kubo write bleach or what was the purpose of it, what were the goals the MC wanted to achieve, I can bet Kubo cannot answer. Somewhere during this clusterfuck of keeping a failing plot alive by nonsense plot devices, he forgot why he was writing. He forgot who these characters were. He forgot who is reading this manga, who is the core demographic. He forgot the message Ichigo was going to tell. But most of all he forgot to respect his own creation and giving it the closure it deserved. And so bleach is a story that tells itself in first half and reverses itself in second half, and if this sentence made no sense to you, congratulations, you figured out exactly what bleach manga is.
Bleach is not the first and will not be the last manga with superior potential that tanked due to poor writing. What makes bleach unique is how monumentally bad the fall was and how truly crazy Tite Kubo is to knowingly bring his manga back to square one. I wish I could say it was the mad hatter kind of crazy for those of you who love chaos and lack of logic, but with 700+ chapters of mediocrity, slow reading and lack of plot, it's the kind of crazy you don't want to deal with.
With that, this bleach fan... oops.. this EX bleach fan, signs off.
