OP, him becoming more of an asshole is one of the smallest problems of the show. Surprised you didn't bitch about Rita since that seemed to have been what most people bitched about forever, while many of those same people gobbled up Skyler in Breaking Bad even though she was practically the same fucking character and easily as annoying and frankly Skyler's actions actually make less sense than Rita's.
Plus, I can't fathom how basically no one else takes issue with the absolutely massive plot hole from the end of season 1 that the writers pretend didn't happen until they had to try and finish out the show. Every season after that was basically just padding the show out until it started to wane in popularity and they had to finish it off.
Dexter really seemed to be a show that had a thought out conclusion and was likely only meant to be a few seasons long until it got popular and then it turned into typical Showtime show ("risque" plot, T&A). I'd say Dexter was about the best of that breed, but it never lived up to the promise that the first season offered.