I'm surprised that people are having trouble getting into The Poison Master. I picked it up on a whim at the library and pretty much read straight through it in an afternoon. I thought it was awesome, both characters and setting(s). Liz Williams comes up with such interesting ideas! The worldbuilding was particularly impressive, I thought, and I like the inclusion of bits of Elizabethan alchemy and lore.
I love the ending. Ambiguous, but hopeful. It reminded me a bit of Vivian Vande Velde's bittersweet endings, actually, although their writing is otherwise nothing alike, and it's just a nice change from uncomplicated happy endings.