Like cassidym, I too have read all of them and enjoyed them all. They're not literary masterpieces by any means, but they are good reads for when you don't necessarily want to think too hard
I think I must be a very inattentive reader though. I didn't. Notice the short. Sentences. Mentioned. Above. Nor did I notice the changing POV of the books (and I read most of them back-to-back). I guess I just got into the story and didn't notice the way it was written.
There was also a note at the end of the last one (
61 Hours) saying that the next one is due out in November 2010.