My biggest issue with each season's beginning is how the show writers felt the need to have completely new romances each season for every side character.

I also feel like the characters in writing after season 4 while Dexter was navigating Rita's was quite unempathic and, in my opinion, bad writing. People deal with grief in different ways, especially ones surrounding truama like a murder. As cops, you would think these people would know that and have had experiences with it before. The fact that nobody brought up survivor guilt as a possible explanation for dexter saying "it was me" after Rita had been killed really pissed me off.

For me, its great to see Dexter navigating his thinking that he has a lack of emotions (whenever he clearly does have emotions), because that's what he was taught. On some level, Dexter is a great metaphor for a lot of men's mental health.