Dexter was fantastic. Unfortunately, like with a lot of anime, they decided to ignore the written part of the story. If you didn't know, Dexter is based on a series of novels that just recently ended by Jeff Lindsay. The first season of Dexter is almost true to the novel. Pretty darned close. After that, it's like HBO said, "Hey, lets make Dexter make the same mistake a few times in which he reveals his secret to someone and it obviously bites him in the ass."
The season 4 was fucking amazing. It was as good as book 2 or book 4 (We don't speak of book 3, which was basically Jeff Lindsay saying that the psychopath in Dexter was literally a demon/fucking who cares. For a while, the "Dark Passenger" which is what Dexter calls his need to kill, was a literal thing. Something with wings. It works okay mostly, he has a sense for figuring out who thew nut jobs of society are. His passenger reacts to other weirdos. But really, book 3 was like, "It's not just Dexter's gut. Its for real!"
I liked book 4. It had to do with cannibals. Season 4 of Dexter was, quite literally, some of the best TV I have ever seen. I won't spoil stuff, but seriously, if you haven't seen this far, go for it.
After that, it's just Dexter making the same fucking mistake every season. "OMG hot girl, let me fuck her and then tell her about my hobby of being a killer." Every time it bites him in the ass. And it is boooooooooring. Oh god, this time he tells a GUY his secret? So new!
In addition, the books actually had interesting antagonists. The second book is my favorite. He plays hangman with his victims and cuts off a limb for every letter they get wrong. He leaves them alive without their tongue, eyelids, or limbs. The show never got the damned dark. Book 2 kicked ass along with book 4.
I'm going on a rant here, which wasn't my intent. The show was decent. and it was great for seasons 1 and 4. Like, superb. But it ended up being a show that I think the producers felt like waiting for Lindsay's stories, so they rushed stuff and a lot of the seasons felt really generic or repetitive.