I get that a study of the relationship between the husband and wife was a key part of the story this year, but I felt they spent way too much time on that, dragging it out longer than it needed to be. It's not like we didn't know they got together in the '80s, had trouble in the '90s, and then she died sometime between then and now. Some of it made sense, but so much of the last episode seemed focused on that, when I was much more interested in the story.
I was a little frustrated that the main mystery's reveal was done for exposition, for the most part. I had it pieced together for the most part (except for why they killed the boy), but it was still someone sitting down and telling them what happened rather than the detectives figuring it out, even though the audience had. I also felt like they made it almost too easy for us to figure out, as opposed to season one (in which the murderer was a minor character who had one scene in the first seven episodes) or season two (in which the whole season made very little sense, but the actual murderer was someone who was never a suspect and had a motive we couldn't have possibly figured out).
The memory loss issue seemed a little gimmicky, to keep both us and Wayne in the dark longer than it needed. I liked the idea, but it got a little frustrating with how it kind of clicked in and out when convenient to the story. I guess that's a little bit about how it actually works, but it still felt like a clumsy mechanic at times. Which brings me to...
I'm also unsure how to feel about the fact that Julie Purcell is actually alive, but none of the main characters know it - only the audience (and Julie and her husband and maybe some nuns) know. I guess it doesn't really do anybody else any good to know, but that's a lot of buildup for no emotional payoff, really.
Wayne randomly running into Julie's current husband, striking up an unnecessary conversation in which he revealed exactly the necessary information, and the book falling open to the exact page also felt like some extreme deus ex machina. I'm rather see good police work pay off.