While riding the train, some girls get into trouble.

Why is Bleach such a great anime?

It's one of my favorites, though not my all-time favorite.
It's one of the shows I liked the most, even though I didn't think it was all that good in retrospect. I liked it mainly because I found it refreshing to watch a shonen show that didn't feature an idiot protagonist who was always at some extreme on the emotional spectrum. One of these is not like the others. Ichigo is a much more mature character at the start of the show than the other protagonists of the Three Pillars of Shonen Jump (Naruto and Luffy are the others, for those who don't know) at the start of their shows.
Unlike the two, he is a reliable older brother character who is intelligent, does well in school, and is still a kind person.
He's the kind of guy you look up to and want to be, while Naruto and Luffy try to appeal to you as you are now. You might think that that last line would make it seem like the latter two are more relatable, but that's actually false, because unlike the other Jump mainstays, Ichigo actually has a real family. Lazier authors will make their protagonists orphans ostensibly to do away with the hassle of building a story around a family who can weigh the hero down with emotional burdens and perhaps cause them to hesitate when the going gets tough.
Kubo Tite, Bleach's mangaka, has instead made every member of the Kurosaki family powerful enough to fend for themselves, giving Ichigo the peace of mind he needs to fight at a hundred percent.
Adding this to the fact that it's at least partly set in the real world, and we can say that Ichigo is actually a more relatable character. The Kurosaki family That's my main reason, so are there any others? Hell yeah. Bleach, unlike the other two, is a chanbara anime, which specifically means that the characters fight with swords.
Yes, there are characters with swords in both of the others, very notably Zoro in One Piece, but those are the exception rather than the rule.
I like swords.
I like that the swords have cool, unique names, and that they do cool, unique things when you say some cool, unique words. ALL THE SWORDS! I also like that the main characters on the show are basically military officers.
I'll make it very clear that I am a pacifist, but I still like to romanticize warriors and soldiers and the like.
I find it cool that the main characters are part of 13 elite military squads with their own philosophies, rules, discipline, tradition and mythos, and not just a ragtag bunch of kooky weirdos.
The same thing is present in Naruto to some extent, but the concept doesn't seem to be as fleshed out as it is in Bleach as it's simply a hierarchical system that focuses more on small three-man cells than a military establishment. Of course, Bleach also has some things that the others have, such as the typical shonen trope of "power rankings", notably in the Arrancar arc where you have the villain group's ranks literally tattooed on their bodies.
I'm not sure if this was supposed to be some sort of meta kind of mockery of this particular shonen trope--given how Kubo names his mini-arcs in the manga, I wouldn't put this beyond him--but I like it. The Ten Espada In the end, I think the synthesis of these elements, plus some I didn't mention because it would take far too long to describe all the things I like about this show, makes Bleach a show with a target audience age a bit above the ones for Naruto and One Piece, from the art style that places emphasis on uniforms to the story elements--Ichigo stabs himself in the heart in the very first episode, for example. I like shows that are a bit more mature than the average, while I think the other two cater more to the average level of maturity (or lack thereof). And that's why I think Bleach is so great.