In manga, I generally go for a decently well-developed plot, memorable and strong characters, and nice art. I don’t care as much for action scenes or badassness, and if I had to choose, characters would be more important than plot. So I'm just first saying the rating will vary extremely based on what you care about.
Bleach was best at the Soul Society arc, which I'm pretty sure 95% of people would agree with, but like most mainstream shounen series, it falls in overall quality/pacing as we go hundreds of chapters in. The plot at the beginning was more interesting, and the progression was suspenseful and exciting, but then Kubo-sensei kinda loses it a little and starts writing random arcs. The HM arc was pretty much a repeat of SS, so that was tedious to wait through, but I managed. As for the art, it’s pretty solid in my opinion, and I like the style much better than Naruto's. More depth and much better anatomy.
Here's the meat of my opinion of Bleach. To me, certain characters and relationships alone make Bleach worth reading. For other series I’d complain about the plot or pacing or this or that, but Kubo has made me shut my mouth. I know, this series doesn't probe challenging moral issues like in Death Note or Code Geass ect, nor does it artfully deal with characters with severe psychological problems like those in Neon Genesis Evangelion, but I adore Kubo’s storytelling style the most. His word choice and dialogue convey the characters’ emotions very well - I can feel connections with characters in Bleach more than any other series I've read. The way he goes into the characters' minds is quite deep and realistic and though there are a bit too many to keep up with, most people can identify with at least a few.
Personally, I adore Rukia's character and her unique relationship with Ichigo. Rukia is an absolute breath of fresh air – her personality can’t be found anywhere else and she puts all other heroines – shounen and shoujo alike – to shame (with very few exceptions). An extremely strong character, not necessarily physically, but mentally/emotionally. Every time Ichigo loses his cool, she can kick him in gear again because they are in such synch with each other. It sounds contrived in words, but is portrayed very naturally and uniquely throughout the manga. Simply unparalleled. I absolutely love the artful subtlety and even though they don’t share screen time often, Kubo has never lost his touch with their interactions. I honestly feel like Ichigo and Rukia’s relationship is the backbone of the entire story, and the main reason I kept reading all these years. If I had to quit every manga series but one, I’d hold onto Bleach just for this one reason. But that’s just me. And though emotional elements play a bigger part in this series than most mainstream shounen, I don’t think it gets distracting for people who are more into action. Not at all. (Well, maybe the action is sucking at the moment, but that’s a different story.) Bleach has gotten worse from a critical standpoint, but it’s going back up, and I will never complain about anything because I believe in Kubo’s skills to recover. I read his story because I appreciate certain skills of his, so I am perfectly fine with ignoring the flaws of Bleach in exchange for its better elements.