It always irritated me hearing people say he started acting out of character as the seasons went on. Dexter was a cold, calculating, heartless/ruthless dude for all but 6 episodes of the first season. Letting a young killer go because he identified with him; passing out from a room of blood; wanting a "normal life" with Rita; being heart broken over killing his brother and letting a killer go; bonding with Lila because she was like him; beating the shyt out of the dude that killed his mother leaving DNA all over the place. Dude was doing all types of "uncharacteristic" shyt in the first two seasons to whatever everyone else romanticized this show and the character to be about. That's not even speaking on him making best friends with an ADA, killing with an ADA and driving around with a fukking killer on Thanksgiving.
The writers were always open about this show being about his growth and riding the line between being human and a monster. While I personally hated season 5 and didn't like season 8, the finale was as apt as anything else. More artsy and not as clear cut as what most would feel the ending should've been, which is him getting arrested? Sure. But the idea of Dexter going into a self-imposed exile because of the things he's been responsible for was just as if not more appropriate for the story they told the entire series. The show was never about the cat and mouse game like Walter White - if it was, LaGuerta would've been in that spot from the end of season 2, even more so after season 3 and completely on his ass at the end of season 4. Instead they continued to center the show on Dexter's ability to live the double life.
Dexter did a lot of the outlandish shyt the first few seasons and it didn't take away the quality of the show. The poorest seasons just had uninteresting storylines with uninteresting characters that no one cared about. No one gave a shyt about Julia Stiles in season 5 after Rita just got killed. Season 6 was nothing but a connector to the end game, which honestly could've been season 5 to salvage things. Season 7 had a lot of great things in Louis Greene and Isaak, but they ultimately surrounded it around a love interest that, again, no one care about. 8 had potential after LaGuerta got killed to get on to the track of Dexter being found out, but again, that wasn't the story they wanted to tell, because they focused on the love story no one cared about. They killed off the interesting characters in the name of telling the story of Dexter evolving but it just wasn't a very interesting one.
If I could retell the story, I would keep Brian alive and have him be vengeful after Dexter saved Deb, killing any and every body that mattered to Dexter in the background and make Dexter vulnerable in that way. Have him responsible for Doakes's death by leading Lila to him in the cabin; have him be in Prado's back pocket, not the Skinner. Have him clue in Trinity to kill Rita. Have him raise suspicion that BHB was still alive after Doakes died, to keep LaGuerta suspicious. Have him responsible for LaGuera's death eventually. Have the most of the same characters (minus the season 5 and 6 killers) appear but have Brian responsible for shyt, with Dexter getting the suspicion. Eventually a show down between the 2 with Deb finding out and being killed in the process - leading to Dexter exiling himself because he is indirectly responsible for everything that happened by letting Brian live. That would've been much more impactful because the central characters remained in tact - not randoms we were supposed to just like just because. I think that could've been stretched the same amount of seasons and kept characters credible.