I just finished the final book in the series last week. While I enjoyed the first four or five books just fine, I understand where people really felt they weren't that good past the first book, which was undoubtedly the best of them.
I'm not sure how this will turn into a TV series. Without the much darker aspects found, I'm not sure how much impact it can have. That is what I found with the books. They delved into some really dark places and the heroes manage to persevere. Without that contrast, I think the series will fall flat regardless of director.