Wow. I thought this was an outstanding movie. It definitely does the book justice. The film stays very true to the feel of the book. I never really felt like anything was taken away in place of some movie magic.
Obviously it wasn't a perfect image from the book, but it did very well. The only things that I flat out didn't like was that they changed the 'Receiver' gene from being pale eyes to a birthmark, which makes much less sense to me.
I did enjoy the ending more than the books. It felt more complete. The book leaves you wondering what is real and what happens in the Community. The movie shows that aspect much more fully.
Fantastic movie.

Also, I believe it is called a quartet, not a quadrilogy. I also have not read any of the sequels. I never even knew they existed.