I've read the whole series, except the final entry released last week. my wife has read it and is dying to discuse it, but I'm still unable to read.
the story is interesting, with good characters but it is writen to be easily understood ( I'm not exactly sure how to put this, other than - you wouldn't have to have a high reading comprehension ability to follow it).
still it's very entertaining without compromising the message. interesting, likable (and hateable) characters.
IMO the first 4 or 5 books where the best, the last one I read (not the latest release) seemed like they rushed it to get it in by deadline. with situations not fully developed and characters doing things that where completely out of character for them in order to get them into positions they needed for the story to advance.
all in all a very good read for those interested in Christian fiction. but you wouldn't have to be a Christian to enjoy the story.