Firstly I've enjoyed watching Happy Valley overall but in the same way The Killing became a bit cliched I think the same thing happened here. The writer should be congratulated for avoiding an all guns blazing Hollywood neat and tidy wrap up but the journey to the climax was a bit frustrating and unlikely. At least the main villain TLR was presented in more complexity and was able to display some humanity.
For the plot to work our heroine has to do the most stupid and irresponsible things and ignore basic police protocol - something that we can see in many of the other previous episodes is that she plays generally by the book. That is a bit of a let down and feels very contrived.
The subplots in this season also get jettisoned and are not resolved in a satisfactory manner - why spend so much time on them if you then hastily wrap them all up in about 20 seconds. They were quite intriguing and I felt deserved a bit more air time.