Not really a knock on the show, but more of an annoyance.
I can't shake the feeling that the show expects you to assume too much within the realm of fantasy and reality(I forget the literary term for this). Its like they expect you to believe that all of this stuff is just a mere coincidence far too often, and it tests that feeling a lot. Believable that Brian was a serial killer maybe. Then he just happens to run into the arsonist Lila and accidentally kills Miguel Prado's brother. The Trinity killings kind of make sense within context because there's been a small build up for that with Agent Lundy.
They've already used Dexter's brother as an angle, the femme fatale angle with Lila, the sidekick angle with Prado, and finally a legit serial killer with Trinity, so now its time to actually explore the darker angle of Dexter himself.
I am aware that we wouldn't have a show if Dexter didn't meet these people, but it still feels kinda cliche to me. It'll be interesting to see what he does with his son, since Dexter himself is struggling with his own code.