I've read the first three. it starts off good, but in my opinion the series stars to drag by the middle of the second book. I think book three will be the last one I read.
I've had the same reaction to the author's Weather Warden series, as well. After the first couple of books, I lost interest in reading any more.
I just finished reading number 7, waiting on #8. If you think of them as serials and not novels, it goes easier. Don't expect them to wrap up by the end. Five was...not good (it so needed to wrap that set at the end), but I think she had health issues at the time, and six and seven are awesome (though I would have preferred a different villain for 7). Two was a little...eh...feel like you want to take a shower afterwards, but overall I love her writing style and simile originality. There are a number of free short stories on her websites that fit between each novel as well (the one with the motel demon is my favorite).