4. Phelps Is Still Alive... And The Villain (Mission: Impossible)
Easily the most controversial plot point in the entire M:I series is the reveal that IMF team leader Jim Phelps (Jon Voight) is, in fact, the mole, and murdered three IMF agents at the start of the movie. In the TV series, Phelps (Peter Graves) was the IMF's Director and an indefatigable good guy, so to see such an iconic staple of the series turned into a crazy terrorist rubbed a lot of fans the wrong way, and many of the show's cast, including Graves himself, expressed disappointment at such a radical twist. Does it work for the film on its own terms? Absolutely. The movie is its own beast so it's best to just separate it from the TV show, but even so, it's a wildly unexpected turn and understandable that not everybody was on board with it.