9. "The Getaway" (Season 4, Episode 12) - Dexter
The finale of Dexter's fourth season is one of the series' best-ever episodes, concluding with Dexter (Michael C. Hall) offing the Trinity Killer (John Lithgow), and deciding that his desire to live a normal family life is finally overcoming his desire to kill.
But tragedy strikes in the episode's final moments, as Dexter returns home to find his wife Rita (Julie Benz) slain in the bathtub, with their son Harrison lying in a pool of her blood nearby.
This wasn't just a shocking ending, it was a thematically brilliant one that brought Dexter's journey full circle, given that he himself was rescued from the scene of his mother's murder as a child.
And though Rita's death certainly had the potential to shake up the show's formula and give audiences a fiercely unrestrained Dex moving forward, ultimately it signalled the series' creative high point, with the remaining four seasons proving wildly uneven.
This culminated in the near-universally despised series finale, where Dexter's sister Deb (Jennifer Carpenter) dies in woefully unsatisfying fashion, and Dex ends up faking his own death, hiding out in Argentina as a grizzled lumberjack. Right.
While there was virtually zero chance of Showtime agreeing to end Dexter at the height of its popularity, season four's ending is so perfect compared to what followed that you may as well just stop watching right there.