I just don't feel like the character of Fatma is herself well enough fleshed out for me to enjoy the book just for the pleasure of hanging out with her.

Agreed. I'm into this series exclusively for the worldbuilding. And it's textured enough to keep me reading, but I'm really unimpressed with Fatma as a character.

Also in agreement that Tram Car is far and away the best story set in this universe.