3. Stop Trying To Manipulate The Audience
In this great, Internet-sponsored era of hyper scrutinization, it's rare that a series actually pulls off a twist that no one legitimately saw coming. Over the years, many successful shows have risen to the challenge and delivered storylines that still packed an emotional punch whether you predicted the turn of events or not. Such programs are usually character-driven, though, and Dexter is a show that really only has one interesting character, making story and execution all the more crucial.
Unfortunately the writers seemed to think that discovering Gellar was dead and appearing to Travis in the same way that Harry appears to Dexter would be an ultimate, jaw-dropping game-changer of "holy shit" proportions. That big "shock" was revealed at the end of episode nine; most people had already guessed it by the midway point of episode two. And sadly, the surprise itself was all the twist was really predicated on. Whether you called it beforehand or not, the whole "Gellar is just in Travis' sick head" concept had no real effect on anything that came before or after it. It was simply dumb, and even worse, the drawn-out nature of it forced Dexter to behave idiotically.
What's more, it wasn't even a fair twist. Since its fourth season, Dexter has had a new showrunner every year, and the lack of clear vision shows, painfully. Up until this season, we're almost certain that we never observed Ghost Harry appearing to physically interact with anything. This season had Gellar touching objects left and right, and Ghost Brian was even shown "eating" while Dexter rested. Straighten out the rules of your universe, guys.