As friends have opined, Marla comes off better on her home turf, where she is the generally-aggravated but not-usually-sociopathic gang leader for a gang of powerful magicians who would all be worse for civilization than she is. Also, she interacts with very few muggles in this book (the one nonmagical major character, she is completely fair with). I don't mind so much when she is vindictive and mighty-makes-righty towards other sorcerers, because that's clearly their social norm.
So my problem has been clarified: I get very little sense of Marla caring about anybody or anything. (See earlier reviews about the brutal-hero thing.) Story events try to demonstrate it -- she cares about her assistants, she cares about her city, these are crucial plot points -- but each time it feels out of place with the narration. We are told that she kills only as a last resort, and my response is "really? uh, I guess." Maybe this is on purpose; not all of the characters in the book buy it either.
I think it's a ground-level stylistic thing, really. The author is doing third-person intimate without the intimacy -- at least, that's how it comes across to me. No doubt fans would say she's doing it without the wallowing in angst and maudlinry. (I just started the thirteenth-ish Weather Warden book, so clearly I have no claim to restraint or subtlety.)
Anyhow, the fireworks are exciting enough (this book has assassins, treason, an excellent secretary, and an insane universe-warping dream-weaver on the loose) that I am willing to keep on with the series and see where it goes.