10. "My Finale" (Season 8, Episodes 18 & 19) - Scrubs
While it was being written and filmed, the finale to Scrubs' eighth season was actually intended to be the series finale, with more than 50 prior cast members returning for J.D.'s (Zack Braff) big send-off.
And indeed, "My Finale" was about as perfectly fitting a finale as Scrubs could've given fans.
J.D. leaves Sacred Heart, but not before viewing a film which hints at his happy future with Elliott (Sarah Chalke), where their son gets engaged to Turk (Donald Faison) and Carla's (Judy Reyes) daughter, and J.D. even gets a reluctant hug from Dr. Cox (John C. McGinley).
But ABC made a last-minute decision to renew Scrubs for a ninth season, effectively undoing that sweet and conclusive ending, with a final batch of 13 episodes focused on a new cast of medical students at another hospital, with only Dr. Cox and Turk remaining regular cast members.
Creator Bill Lawrence actually asked ABC to rename the ninth season to "Scrubs Med", considering My Finale to be the end of Scrubs as we knew it, but for branding reasons, ABC refused.
With almost all of the original series' writing staff gone, the quality of season nine evidently suffered, adding a wonky post-script to a beautiful finale that tied everything off terrifically.