Flanagan has a vision that many of us may not see at first. He carried the hardcover version of this book around with him for years while pitching films. Most didn't see a movie in it. He saw more than a movie. He saw something about how some of us spend our lives in the shadow of the sun. It's an essential vision of the mask we sometimes put on our past.
If nothing else, think of it as an addition to everything you know about the other adaptations, with a hope that they make more to flesh it all out a little. What I saw so far worked for me as a mild form of entertainment. It would be much better if it is followed up with more. And much sadder if they don't.