They are wonderful. Must be 10 or more of them. I loved them as a kid, and am now on my third read through to my kids. Baum was quite prolific, despite his health problems.
I find the Harry Potter books very entertaining, and spend quite a bit of time discussing the lessons embedded in it.
Although Mad Mammoth and editor-surveyor and I do not see eye-to-eye on this, I find very clear moral lessons sprinkled throughout the book. I don't think they appreciate that the battle of good and evil on this plain is fought by the available troops, humans, who the Bible says are all born in sin.
There are evil witches as there are evil men, and there are witches who are true, and just, and good as there are men who are are true, and just, and good.
Neither the men nor the witches are 'good enough' for the tastes of some.
IMHO, it is a Sacred Duty to fight evil at every level, even if one is neither perfect nor saved.
If you get a chance grab a copy of John Granger's The Hidden Key to Harry Potter, I think you will find his treatment of the Christian underpinnings of Rowling's work interesting.
(BTW, has anyone mentioned that the witches have school vacations for Christmas and Easter. Heck, our school district doesn't even do that!)