I found the game pretty fun. I really enjoyed playing the first two weeks, although the third week felt tacked on, and I did have to force myself a bit to finish it. The replayability is also pretty good. The bonus chapter is pretty good, and the items/bosses you'll find when looking for the secret reports do add to the experience. However, some of the other bonuses require some grinding, which can take a long time if you don't look at a guide.
Probably the best thing it introduced was the user-controlled difficulty that you could change at basically any time, and I do hope that the general positive feedback of this game inspires more developers to consider options like it.