I know there are some out there that are disappointed that Rita is dead, but I for one am happy. This season she has been especially annoying, and at times has been intolerable, so her death will remove one of what I see as a problem with the show. It also allows the writers to expand the character of Dexter. In the episode we see a huge shift in what he wants. Dexter wants the most to rid himself of the Dark Passenger and just be normal. But normal doesn't fit in the world of Dexter. The stimulus of Rita's murder will compel Dexter to new depths we haven't seen before, and I'm sure the writers are salivating at what they can come up with.
The episode had twists and turns all over the place and left me wondering if the next thing would be the huge twist everyone was talking about. First it was Quinn getting more obnoxious and he could have done something crazy. Second, there was Dexter getting arrested and going to jail, and he easily could have gotten caught in one way or another. Then he almost gets caught at the Mitchell's house and nobody realizes he got into a locked garage. Finally Deb tells Dexter about his connection to the Ice Truck Killer, but doesn't make the connections to Dexter.
Instead as it was all winding down -- the Trinity Killer dead, Rita waiting to go on their honeymoon -- Dexter arrives home, and in the final minutes discovers his son lying in a pool of blood and a dead Rita in the tub. The juxtaposition of Dexter birth into blood and Harrison's was fitting and left an indelible mark on a fantastic season finale.
Dexter has had its ups and downs (mostly downs in recent years), but season 4 redeemed itself from the forgettable third season which I did not even finish. The season finale set up season 5 better than any other season finale before it, and left everyone who watched it wanting more. If you watched the season finale and don't want to continue watching, you have a screw loose. I've had plenty of criticisms for the show and some angry comments directed at me for not loving the show, but in the end, I was thoroughly pleased. Bravo to everyone involved.