Let me start out by just doing this briefly and if you want you can read the much longer part.
Story- The story started out fairly weak and episodic in the first section. Then the second section was decent and began some really interesting things. However, the third section could not manage to completely follow through, and the main plot line for the majority of the manga falls apart completely by the end of this section. Ever since then the author introduced a completely new set of antagonists that seem largely unrelated to anything that happened before, but it's clear at this point that the series has just gone on for way too long.
Art- The art starts out very very weak but he improves steadily as the manga goes on until by the 300th chapter it was quite solid. It has only continued to get better since then.
Character- There are lots of interesting characters in Bleach, but the main character tends to fall a little flat sometimes. Anyway there are very few who I would consider to be genuinely unlikable and in MOST cases he even gives you some insight into what the antagonists motivations are. (But not all, and he is especially bad about this with his main antagonists, for whom it's most important).
Enjoyment- Many exciting fight scenes, if you're into that kind of thing, and there is quite a bit of light-hearted comedy here and there. Generally up until near the end it's a fun manga to read.
Overall- Read more below, but basically it was fun for a while but never really delivered on it's potential.
I'm going to take you through the experience of Bleach as I experienced it, while reading it, so you can understand exactly why it was so popular for a while, but now has gotten so much hate. It's something that happens a lot in long series, so it's not like this progression is anything new.
Spoilers in large numbers will follow. This is also really long, but I mean the manga is like 500+ chapters so, what can you do?
-ARC 1 - THE HIGHSCHOOL KIDS DEMON HUNTING MANGA-
So I started reading Bleach like 5 years ago and no lie, I dropped it after chapter 10 and didn't try to read it again for more than a year. The reason was because I felt that the art was laughably bad. At the same level as the first few chapters of Shingeki no Kyojin, but without that series far superior plot and characters. It was this fairly poorly drawn manga about this boy who can see spirits, and meets a spirit-girl who gives him spirit hunting superpowers. They have fun adventures together with his quirky classmates and funny little sisters and it's all fairly lighthearted and good times. I gave it a second chance a few months later and found it to be diverting, but not exactly a masterpiece. But then at the end, some bad shit goes down, the spirit girl gets kidnapped, and the MC is left at the brink of death by the character who is going to be the antagonist of the next arc.
So yeah the first arc is like a very lighthearted ghost hunting mystery story. There's nothing particularly dark and only VERY vague hints at something bigger going on. That ending though...it pulls you in because you got to like Rukia so much, of course you have to know if she's okay.
Which leads us in to the second part of the story, which most fans will tell you is "the good part" because it is the story most fans were looking for from the beginning.
-ARC 2 - THE SHONEN ACTION MANGA-
So in the second arc, the MC has to rescue his little cutie spirit girlfriend, so he gets himself all powered up and goes to the spirit world to rescue her. In the spirit world he goes though a VERY standard set of Shonen Action Hero steps to doing this, involving fights that he loses at first, then goes and does some training and then winds the second round, or just rallies his resolve and manages to overcome the odds. Finally against an implacably powerful foe, he pulls out some turly crazy demon-like powers and manages to win, but he holds back from actually killing his opponent, instead coming to an understanding with them and rescuing his little girlfriend just in the nick of time!
At the same time, there is this murder mystery going on, and THIS, THIS is where the trouble for this series started, although no one knew that at the time. So at the very end, after saving the girl, suddenly this asshole shows up and stabs the MC in the stomach, then just sort of struts off, saying that he'll see everyone in 3 months when there's gonna be a bigass war.
So once again, the arc ends with the main character getting stabbed by the person who is presumably going to be the main villain of the next arc.
This second part is pretty much the classic shonen action series. The story advances by way of a number of unique battles that the MC has to fight against increasingly powerful opponents, with all the expected last minute powerups and speeches about ones resolve to fight and all that. Also as a side note, the art in Bleach steadily improves as it goes on, and so by the time we got to the middle of this arc, it had reached a level that was really pretty great.
There are also a large number of colorful and interesting characters introduced, and the cosmology of the setting really gets fleshed out a lot.
And the whole murder mystery plot SEEMED really cool, with lots of potential for interesting future developments.
I have to say, if the series had ended with the MC saving the girl and going home to live out the rest of his life in peace, Bleach would have been a pretty decent entry into the shonen genre, there would have been a neat 50-100 episode anime based on it, and people would still be writing fanfiction forever.
If only they could have been content with this.
-ARC 3 - THAT LAST ARC SOLD REALLY WELL SO MAYBE WE'LL JUST DO THAT AGAIN...ONLY THIS TIME MAKE THE ENEMIES SCARIER-
So in the third arc many of the characters who were antagonists in the second arc are now on the MC's side, helping him out. And since the villain ran off to the world of darkness and evil spirits, he now has a bunch of really REALLY vicious monsters working for him.
And here is where things begin to go off the rails. The monsters from the demon world are more powerful than previous enemies (Of course, because this is a shonen action series) so the story just becomes a retread of the previous arc, with the main character losing fights, then training and powering up, all ground that has pretty much been covered before. They even kidnap one of the female characters, taking her off to be imprisoned in the demon world for some unknown (but presumably nefarious) purpose. Just like in the previous arc, the MC has to go to the demon world to save her.
So the problems begin when they have nearly finished fighting their way through the demon world and finally find the kidnapped girl.
First of all, while they were trying to rescue her, there was a good deal of time spent on showing the reader what she was doing while she was stuck there, basically being psychologically abused by, and subsequently developing stockholm syndrome for the demon henchman who was in charge of holding her prisoner. I'm not sure if the author just liked this demon character a lot, or if the fans really liked him, but he just got more and more out of control powerful and unstoppable and unbeatable as the story went on. So FINALLY the MC manages to defeat this unbeatable demon by using another crazy shonen action hero powerup. But the thing was, that because you had gotten all these scenes that involved this demon, you had a feeling for his personality: so when the MC and this demon finally had their final battle, you felt like you knew both of the characters and so it mattered who won and how it happened. Anyway the MC eventually wins, and saves the girl. BUT, instead of the story ending, then he has to go fight the MAIN villain.
So then the author remembered, I guess, that this unbeatably powerful demon who was just killed was supposed to have been WORKING for the main villain. So the main villain, then, by default, MUST be more powerful than this all-powerful unbeatable demon.
Thus ensues one of the most ridiculous case of a Villain-Sue that has been seen in a comic book this decade. The shonen action powerups just get more and more ridiculous, random, and insane. Most of the original cast just kind of disappears into the background, and everyone's power levels go completely off-kilter just so that it can be established that yes, really, this villain is really the most powerful being in the universe. But the problem isn't weather this guy is more powerful. The problem is that HE wasn't the one who we got to know over the course of this story arc, instead all the character time was given over to his various demon henchmen. Since we don't actually know what this villain's motivations are, or anything about him other than that he's a jackass Villain-Sue, nobody wants to see him fight: by this point I'm pretty sure everyone reading the manga was just sick of him, and wanted him to die already.
Anyway eventually the author actually had to resort to sending the MC into an alternate dimension where time moved more quickly so he could get 3 months of training into and hour of subjective time. EVEN THEN the villain was so powerful that after no less than 6 mid-battle power-ups and transformations, he couldn't actually be killed and could only be imprisoned, and just to do that, the MC used an attack so powerful that he went into a coma for three months and lost all of his powers.
And really, where can anyone go from there? When you have used a villain who is so powerful that he literally cannot be killed, there just isn't anywhere else you can go with a shonen action series. But by this time the artwork was finally looking really really solid, and bleach was still making buckets of money.
So of course they had to continue it.
As of now they're about 3-4ths of the way through the 4th and allegedly final story arc, and I know it's about 3/4ths of the way through, because it is all just the same story as last time, just with an even more ridiculously over-powered group of villains who the main character will likely once again have to pull out all sorts of crazy bullshit to defeat.
The thing that I think frustrates most people was that they got really hyped up for the end of the third arc and then it just never delivered. The second part of the story was really good, and then it set the next arc up as being this big epic battle, but that big epic battle took like 200 chapters to get to, and wound up just being a whole bunch of bullshit. A lot of hints were dropped about things that might turn out to be true later, but then a lot of them got dropped or were just picked up again in weird ways.
