A Master of Djinn 3: The Characters
There was a huge cast of characters here, considerably larger than many books I have read recently. Did you find that effective or confusing? How about the blend of human and (various kinds of) supernatural entities?

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Comments
I found the large cast effective. I liked all the characters, and enjoyed their interactions.
I think the large cast worked well. I think Clark did a good job of making even the minor characters distinct, so I didn't find myself getting confused by who was who. That was in terms of appearance, name, mannerisms, and character and goal. Even though we didn't know much about the minor characters, each of them came across as someone that had a deeper life; it's just that we didn't have time to know them better.
I especially liked that our first impression of each character was their clothing: I thought that was a nice touch to show Fatma's outlook.
Yes! I thought much the same*! Clothing was vital to Fatma, and it was how the world revealed itself to her! Deft touch! Nice catch Neil!
How about the different levels of interest that the djinn showed in human affairs, ranging from utter disinterest through to collaborative work on big projects and (so we learn part-way through) intimate relationships?
That is traditional with Djinn. Some avoid humanity, some mingle with humanity, and some mingle even closer.
I'm not sure the "clothing is the first thing you see" is a cultural thing so much as specific to Fatma and her outlook. That said, my impression is that Middle East people are more formal than Europeans: people dress well and formally, people are addressed by title, people speak politely, hospitality is important. At least, that's in formal settings: there's plenty of informal life going on as well!
But, related to that, it's a shame that we didn't get any breakthroughs in the case because of something to do with clothing.