I realized after said I was enjoying The 13 Treasures that I did not give any specifics, yet I was extremely precise when outlining what I did not like about The Weird Sisters.
So...
1. The main charater Tanya is well-developed and realistic. She behaves the way a 13 year-old (Hmmm, coincidence that she is 13 and all the books revolve around 13??) who can see fairies might.
2. The secondary characters are real characters, not just cardboard stand ups who come in to the scene, say their lines to propel the action, then leave; they are interesting and important.
3. The dialogue is natural without being too casual. I like it when fantasy novels avoid slang and colloquialism. It makes the books more enduring, but it also takes them out of this world and places them in a world that is not quite like ours. This was one of my problems with Episodes I, II, and III of the Star Wars saga..too many contemporary phrases and words that seem out of place in a galaxy far, far away a long time ago.
4. The action moves quickly without skimping on details and feeling sparse.
P.S. Yes, I cracked and ordered the next two books from an on-line seller. One coming from NY and the other from the UK.