7. The Office, Season 8 (NBC; September 22, 2011 - May 10, 2012)
No matter how much time the producers have to prepare for it, and despite how game the rest of the cast is to move forward, losing a major cast member is one of the most difficult things for a show to overcome.
Steve Carrell was the indisputable headliner of The Office with his portrayal of Michael Scott, but he'd also become an American comedy icon along the way. Finding humanity in a character like Michael Scott is a great comedic feat, and it's extremely difficult to imagine the show without the sweet sweet ineptitude of Michael Scott. Though The Office has made an amirable effort in Carrell's absence, its post-Michael episodes just feel flat.