http://i1182.photobucket.com/albums/x456/ShadowForce98/Bleach%20Wiki/Arrancar109.png: Depends on the character really, some of them could have had more development, as well as more focus, but at the same time, there are certain timing issues he has to keep in mind. If he didn't, he could probably flesh out many more of them than he has.
The anime does do some of them justice, but that's only up until the Amagai arc in terms of anime arcs. The filler added onto some manga content has helped in some instances, but not overall. The Zanpakutō arc and the Invasion arc were namely about the Shinigami, and all arcs had Ichigo involved more than he should have, especially the Zanpakutō and Invasion arcs.
In other words, the last two arcs heavily lacked character balance.
http://i1182.photobucket.com/albums/x456/ShadowForce98/Bleach%20Wiki/Godisme.png: Kubo is not really the best with character development. Usually only one character gets any development in any arc and it’s never who needs it. And the anime never does justice to anything.
http://i1182.photobucket.com/albums/x456/ShadowForce98/Bleach%20Wiki/Xilinoc.png: On the whole, he handles them fairly well. Pre-timeskip, with the aforementioned exception of the Espada, he took the time to explore many of the characters, and for those he didn't expand upon, he dropped hints at (i.e. Unohana, Yamamato, etc.), but he didn't always do it right (i.e. Gin and his motives being introduced right before his death). Post-timeskip, it hasn't gone quite as well. Tsukishima and Ginjō, though they were the central antagonists of the previous arc, weren't developed as much as I had hoped, though we may see more of them in the current arc. And speaking of the current arc, the new villains haven't been defined anywhere near enough. We still don't know their motives, their past, or their real power. In terms of anime, for the most part, it does an okay job of creating realistic backstories for characters we may not know much about, and occasionally manages to develop them within the current storyline, which is nice.
http://i1182.photobucket.com/albums/x456/ShadowForce98/Bleach%20Wiki/Salubri.png: Kubo once said in an interview, and I believe, that he loves all his characters and especially the one people dislike. I appreciate that and understand it. As far as the way he handles his characters, well he has a large cast of characters and he shows preference to the more prominent ones and less so to a particular group, namely the human characters. As far as development it’s hard to say some characters do get development while most tend to have instances where you learn something about their past or personality, but then those characters just continue on as previously, showing no real growth. In other words the development seems fleeting for some and temporary at best. In other characters they grow considerably and in meaningful ways, especially considering their importance in the story. The anime commonly distances itself from development unless it needs to fill in space. In those instances it’s hit or miss, sometimes the character acts like himself/herself other times they don't at all.
http://i1182.photobucket.com/albums/x456/ShadowForce98/Bleach%20Wiki/Mohrpheus.png: With so many characters, it is difficult to give everyone the spotlight, but Kubo does manage to give everyone their moment, even if they are few and far between. Individually, most of them are pretty well developed. When it comes to expanding on the characters, I feel that the anime tends to be subpar. It usually tries to do so by introducing new characters to interact with them, which is counterproductive since it inflates the cast even more.
http://i1182.photobucket.com/albums/x456/ShadowForce98/Bleach%20Wiki/Lemursrule.png: Overall (about 95% of the time) I feel Kubo has a good handle on the characters. Yeah there are tunes where characters could be more developed, but Kubo can't change certain characters too much so that people (maybe) disinterested in them. I feel the characters who‘re truly relevant are developed. Anime only stories...sometimes yes, but most of the time, no. Going back to adaptations, sometimes subtleties are lost, especially in characters. The characters being stereotypes (example Rangiku, who in the anime is portayed mostly as a lazy, drunk bimbo) and it just displeases me.
http://i1182.photobucket.com/albums/x456/ShadowForce98/Bleach%20Wiki/KuroAshi98.png: Usually it comes down to the character of the day, and even then we only are given small snippets. Ichigo’s relationship with Zangetsu for example comes to mind. Even though Zangetsu resides in his soul and can actively communicate with Ichigo, despite the former’s proven wisdom they rarely actually speak to one another and only when the plot demands it. For such an intimate relationship, it just doesn’t seem that important to either character. Other times, I feel Kubo tries too hard to get around to everyone which weakens the development. It’s why I enjoyed the smaller arcs such as Soul Society, Turn Back the Pendulum and even the fourth movie, Hell Chapter. The cast was varied and interesting, but not so large that it felt like a race to give everyone their fair share. As for the anime-only stories… it really is hit and miss. I’m just going to leave it at that.
http://i1182.photobucket.com/albums/x456/ShadowForce98/Bleach%20Wiki/SunXia.png: In the early days Kubo developed a lot of his characters very well from Rukia's past to Ichigo and Tatsuki's shared past!! However, recent character developments have been lacking!! We still don't know Isshin's past and why Yoruichi is a were-cat!! And we don't even know why the Visored were restored as captains and where the rest of them are, it was just skipped over when it wasn't needed!! In this arc he's been introducing characters and incapacitating them in moments!!
Sometimes anime-only arcs can do well like the relationship between Kon and Nozomi!! However watching episode upon episode of more and more clones gets boring and Ichigo always being the only one who can save the day gets boring as well!! They could do a lot better!!
Too many characters like some lieutenants and many of Ichigo's human friends are ignored!!
: I don’t think character development is Kubo’s strong point. He did have some slowly, with the most being in the Fullbring arc, but we don’t see much character development. Hard to say for the anime-only material, they are so out of canon and have contradictions with the canonical timeline.