A bit easier of a topic to handle than most, but again, there were multiple choices to fill the topic of the day: biggest OMG WTF? season finale. ABC's Lost definitely featured some big OMG WTF? season finale moments, and in particular I'm thinking "Through the Looking Glass" as a prime example of the writers power [although, me being a Season 5 fan, find "The Incident" to be the best OMG! moment]. And if I wanted to be original, I would say the season 3 finale of Supernatural where Dean's deal with the Crossroads Demon comes to pass would be a freakin' great choice. However, I'm gonna seriously have to go with a finale that to this day I remember being utterly amazed by.
The sucky thing about being Jack Bauer is even though you do really bad things for the greater good, one small (or big) bad thing can end up really screwing up the rest of your life. Such a thing occurred at the end of Jack's fifth really, really bad day. Back on Day 4, Jack invaded a Chinese consulate which resulted in one of the Chinese folks dying. Well, one of the Chinese government officials aren't too pleased with that, and try to hunt Bauer down until the end of the day when he fakes his own death and goes on the lamb (as the expression goes).
In the midst of all the crazy shit that happened to Jack all day in his fifth bad day, one would be amazed that there could be any more gigantic twists. Creatively, Day 5 has no predecessor. It's perfect. Brilliant. And then they add these last 15 minutes, and it becomes epic.
The Chinese have, as the government official from Day 4 remarks, "a long memory" (or something like that). Finally, Chang (?) kidnaps Bauer and puts him on a boat heading for China.
I remember being in New York for my 16th birthday, sitting in the hotel room eating Papa Johns with some refreshing Dr. Pepper and being utterly bewildered and gobsmacked by what I just saw. "NO FREAKIN' WAY!!!" Biggest, awesomest, most pleasing finale I had seen up to that point. Those 24 producers sure had balls, and I couldn't be more excited to see where that story went...
From a writing standpoint, it's a beautiful bookend to the first episode of the season, and also a sublime cliffhanger that leaves the viewer wanting more. For every halfway decent to bad episode of 24, Day 5 makes up for every single one of them. Oh, the awesomeness.