I’m sure that it’s not to everyone’s taste. The subject matter is pretty dark. It’s definitely not suitable for pre-teens. But the ending makes it all worthwhile.
If you’re in the mood for a taunt, well-written thriller you should check this out. (Unless you’re one of the aforementioned pre-teens. In that case wait until you’re older. You’ll thank me later.)
I know that some of the fans of the manga are upset that some parts of the original story were left out, but I think an anime adaptation should be judged on its own terms. As it is, it works very well. Perhaps it might have been even better if they had added another cour and put in all the scenes from the manga, but that’s far from certain. One of the most painful lessons that a writer must learn is the importance of making cuts. Generally it’s best to cut out everything that isn’t absolutely essential to the story.