io9 looks at "10 TV Episodes that Changed Television" and it is a very interesting list. One of the episdoes is a great one from Battlestar Gallactica and I couldn't agree more:
Battlestar Galactica, "33"
The Galactica must jump into hyperspace every 33 minutes to avoid being destroyed by Cylons, and the strain begins to drive the crew to the edge of insanity. And meanwhile, the officers struggle with the decision of whether to destroy a civilian ship that's carrying nuclear weapons and failing to communicate. Says Grillo-Marxuach, "This may be the best first episode of a scifi series ever made, and probably the best first episode of any series, period. It set off a run of excellent episodes that was unbroken until the show's second season, and it established a series far more interesting and high-minded than the miniseries ever promised."
Episodes I Would Put on the List
Game of Thrones, "The Pointy End"
I don't want to give any plot points out of fear of spoiling it for some, but let's just say that some things that we take for granted on most shows didn't apply here and I now suspect that they do not apply on all shows going forward. This has been true on the BBC for sometime, but not as much on U.S. shows.
Seinfeld, "The Contest"
Here's the plot from arguably the best show of the series:
After George's mother catches him alone in a somewhat embarrassing situation, Jerry, George, Elaine and Kramer stage a contest to see who can last the longest without any sexual gratification. Temptation quickly sets in for everyone.
Having a whole show based on masturbation, without saying that's explicitly, opened sexual innuendo up to a whole new level. "30 Rock" takes advantage of that every week right now.