If they'd finished, the series, it likely would not have been improved much. The same can be said for every film set that tried the same gimmick outside of the last Harry Potter film. In that case, the first one was the let down. Still, there are worse ways to pass a rainy Sunday. The Hunger Games series, for instance. Too bad the bottom didn't fall out on that series first.
How much one likes this film depends on how much one roots for Woodley as an actress and female heroines in general. It's not a bad film, if it is a let down from the first episode. Take it from this uninspired review that I won't be standing in line to see if it get's better with the next film.