Haven't watched the anime but I loved the manga. Great psychological thriller and the mystery element was fantastic. It was very interesting to see how the plot unfolded and the character development was very well done.
I've heard the anime isn't as good as the manga though. Not sure if there are any particular problems with it but obviously it'll feel more draggy to watch a 74 episode anime than to read an 18 volume manga. I know this was the case with Fullmetal Alchemist: Brotherhood, where it didn't really have major pacing problems but 64 episodes' worth of content just felt a lot longer than it should have since I read the manga first and went through it much faster.