Finished reading it this morning. Like the previous poster, I also enjoyed how the setting was handled with all the references to history, convincing architecture, and so on. The art style was really nice, the characters have a realistic feel to how they are designed, and the art stands out when compared to many other manga series, I think.
Reading Monster was overall very enjoyable, and it was satisfying to receive a more happy ending. I would be interested in knowing more about Johan's state of mind. I did not read this manga very attentively, and I read the whole thing within a short span of time, but I don't believe it was clearly shown whether he really does have a split personality, which was theorized, or if maybe he faked it, or something else. Glad Lunge managed to stay alive until the end. I took a liking to him, beginning with the first scene where he was introduced. His almost smug smile is a sight to behold.
I wonder if things would have taken a turn for the better if Tenma just didn't run from the police after that incident with the adoptive parents and the journalist. He seems to not care about proving his innocence, however his goal would be easier to achieve, if he managed to do it.