Bleach is the spiritual successor to Saint Seiya as they have similar plot structures, story arcs and have pretty characters. The famous Soul Society arc has a similar set up to the Santuary arc as the main characters go to rescue an ally from a fraction the main lead suppose to be a part off. And the antagonists not necessary being evil beings but following orders.
Soul Society feels like the Samurai Era of Japan and the Sanctuary has elements of Ancient Greek. The enemies have rankings with Soul Society having low class Shinigami, Seated Officers and the Captains. Sanctuary has the Bronze Saints, Silver Saints and the Gold Saints.
There are 12 Gold Saints and the priest which equal 13 while there are 13 Captains in Soul Society which are the strongest of their kind and have individual personalities and desires.
The Arrancar arc is somewhat similar to the Poseidon arc but much longer and the TYBW arc is similar in structure to the Hades Chapters.
What Bleach does have over Saint Seiya is the psychological aspect of characters and it plays a far bigger role. Not to mention, female characters are far more active in Bleach while the original Saint Seiya has only a few strong female characters. Both the main leads are also trained by a female character.

The story is about a highschooler Ichigo Kurosaki receiving Shinigami powers (or Soul Reaper powers) from Rukia Kuchiki who got injured protecting him from a monster called Hollow. These Hollows are spirits of the death that weren't able to pass on the afterlife properly and got corrupted turning into vile monsters that consume the people loved the most or beings with high Spiritual Pressure also referred as Reiatsu.
After the power transfer, Rukia was incapable to do her role as Samurai Ghostbuster on her own and had Ichigo assist her in hunting them down. It is a simple story with a great sense of humor and world building as Ichigo learns more about Hollows and how to deal with them as well as his past. See Rukia adapting to the human world as she pretends to be a human until her powers are back.

But the real story starts with the Soul Society arc the stronghold of the Shinigami is revealed. A lot of things are revealed like the crime Rukia committed and Ichigo's desire to repay her for saving his and his families lives.
Various fighting styles and abilities of Shinigami are being explored like the ability to use special powers with their Swords named Zanpakuto. The high ranked Shinigami know the names of their Zanpakuto and can activate them by shouting said name. While the top tier Shinigami have a more powerful technique called the Bankai, a second release.
While it is a simple rescue mission arc, the reasons characters do what they do is giving it some complex elements and the addition of a murder mystery gives intrigue whether someone is pulling the strings from behind or not.
It also set up a lot of things to come hooking readers for more.

However, what came after Soul Society never meets the same high. There are good moments and sometimes good starts to story arcs, the pay off and the lead up is nowhere near as satisfying as the Soul Society arc. There is a reason why many consider it the peak and say that it falls off after said story arc.
For example the arcs after are much bigger in scale and sometimes have complex themes. However, this ends up the story crumbling in its complexity whether it is bad execution, too much information being required for the reader or flat out being discarded for something less interesting.

Powers in the story start as intriguing and well thought out. While it is complex in some aspects, Kubo did a good job in introducing them. The problem arises with the introduction of unique powers per user. At first abilities are simple to understand like Element Manipulation, Swapping Weapons, Reflecting Attacks or Stat Boosts, but later more complex powers are introduced that are hard to convey as images and the author relies too much on dialogue to infodumb the powers by the user allowing opponent’s to find counter measures because said character was stupid for the plot. It is an issue many shonen with complex powers fail at especially when the author uses them in battles that suppose to be fast paced sacrificing tension for a faster pace.
So when the author decides that he doesn’t explain the power of a character in an action scene, it can come off that what you see on a panel is something symbolic or whatever.

Another problem are plottwist in Bleach. Bleach is known as a series for its amazing unexpected but well set up plottwist. One many fans love so much, they try their best to avoid spoiling or mentioning the name of said character.
However, the overuse of plottwist often fires back since Kubo relies in later points in the story so much on it, it feels like it’s done to subvert your expectation for the sake of subverting expectation. At one point throwing away the intended use of a plot device for something far less interesting for the sake to appear smart, only for it to not mattering or ruining what could have been something vastly more interesting. Another example is playing with supposed established information and changing it to something completely different like a weaker character ending up being far more powerful than expected only for that not mattering in the story.
Even going as far as changing the fighting style of an entire race to something the readers weren’t used to.

Bleach fights started as amazing well thought out and unique ranging from rule of cool to analyzing a characters fighting style and using it against them.
Sadly this doesn’t last for long especially in how much power Shinigami have. Shinigami can use spells and the reader doesn’t know what spell who is capable of using. Considering there are 100 destructive spells and 100 defensive spells, any character of the Shinigami force can asspull their way out with a power never mentioned until said point. Not to mention their Zanpakuto abilities and the Bankai. The story also contradicts or give false information what Bankais suppose to be at times which makes you wonder how the regular Zanpakuto ability and the Bankai are related at all.
It gets worse when characters gain additional forms to their Bankai over the course of the story which can give some variety but also can come as another asspull.
The powers becoming complex, something mentioned in a prior section, have also unexpected problems like making the fights a game between two kids saying “Nah ah” or being similar to a kid smashing toys. It will get really repetitive after seeing someone teleport behind someone else “Nothing personal kid” style and either cut through the shoulder or cut off an arm almost every fight.
It gets more stupid when most the enemies the characters are fighting are evil counterparts of oneself in some shape or form.

The manga has also a problem with having way too many characters. Admittedly the power gab between characters are relatively small to something like Dragon Ball meaning a large selection of characters can be useful in battle and even beat a stronger foe. The problem is that each arc introduces at least 8 capable characters and only a fraction gets fleshed out or does something worthwhile.
So it won’t come as no surprise that many of them will get shafted, especially in favor of fan favorite characters like Toshiro Hitsugaya, Byakuya Kuchiki and Zaraki Kenpachi which just happened to be Captain Class Shinigami. There is also Kubo’s favorite character Mayuri Kurotsuchi who solves everything with “science” which ends up being no different than magic in other anime.
Sadly these are side characters and support cast that monopolize most the action away from the main characters which hardly don’t do too much with the exception of Ichigo Kurosaki that affects the plot. Well, and Rukia Kuchiki until after the end of the Soul Society arc where she appears as important but doesn’t have as important of a role.
While this is a massive weakness of Bleach and some characters do end up being clones of each other, there are also a large variety of favorites to choose from and it is almost guarantied someone will be on your favorites.

Ichigo Kurosaki is a great character for the first portion of Bleach. He has his fears and worries but he acts mature for his age and would overcome his issues to help others out. Over the course of the series he would repeatedly get depressed or mindfucked where he quickly loses his will to fight only to get it back through some bullshit. Being done so often can be a total turn off after you got so invested in him.

Rukia Kuchiki is a strong female character in terms of characterization. While she isn’t the most powerful and does rely on others help, she does keep up and provides critical advice to boost the motivation of her comrades. In the first arc, despite losing her powers, she was treated with equal importance to Ichigo. She also has her own mental struggles like her living up to her brothers expectation, the death of someone she looked up to and whether she is worthy to be saved.

Other main characters Uryu Ishida, Sado Chad Yastora and Orihime Inoue appear as if they will have important roles, but their supposed story arcs don’t fully take advantage of them or just drop them like hot potatoes in favor of Captains. They rarely if any play a major importance in the plot.
Especially Orihime who’s treatment gathered her a massive hater following which in turn created a bunch of whiteknights. This also played a role in the ending where a lot of fans got annoyed so much that they burned their manga collection out of spite.

The captains have their own unique backstories and mindsets, but often are shown as people with wisdom or how their responsibilities affect them, even if at first glance didn’t appear as such.

There are also the antagonist which have their own goals and desires.
The hollows started off as people with deep grudges becoming corrupted but over the course of the series they become generic monsters.
The hollow related antagonist start of as a brutal bunch and violent creatures but the ones later seem more reasonable and some becoming actual allies.
The non hollow related ones have the goal to change the world to their desires, want revenge or just follow someone because they have no choice.
There are some good ones but most are not nearly as interesting as the Shinigami who use swords with super powers.

Overall Bleach is a mixed bag of a manga. The side characters overshadow the main cast almost completely with the exception of Ichigo. The fights change from good to repetitive. And the pay off for being invested in later arcs is lacking.
Even then there are a lot of great characters to get invested in with compelling dialogue and cool looking powers. If you are into waifus and husbandos, you will definitively find someone you enjoy.
Kubo is also great at cinematography to build a great atmosphere and setting, but the overuse of one page and too page panels can be off putting later on.