The Least Interesting Mission: Impossible
A producer once said movies are about "moments." I'd say this is especially true for the M:I franchise, where the writing mostly involves connecting the set pieces.
The second film is the most aggressively stupid and ridiculously vain entry, but it has a few moments. One is the rock climbing scene. Another is the fact Hopkins delivers probably the best lines in the franchise. "It's not Mission: Difficult, Mr. Hunt. It's Mission: Impossible." And
Ethan: No. She's got no training for this kind of thing.
Swanbeck: What? To go to bed with a man and lie to him? She's a woman -- she's got all the training she needs.
Compare this with the top-rated IMDb quote for the third:
Ethan Hunt: I'm part of an agency... called the IMF.
Julia: What's that stand for?
Ethan Hunt: Impossible Mission Force.
Julia: [chuckles] Shut up!
There was also the knife-to-the-eye, the motorcycle chase, and the hair. People -- men, especially -- were obsessed with Cruise's hair in this film. The second film also solidified the franchise's marketing, and indeed Cruise-as-Jackie-Chan since. The marketing in the third suffered from the media's relentless Cruise bashing. Jumping on Oprah's coach overshadowed all of his other stunts.
The third movie has a bridge sequence and Hoffman's turn as the best villain, but what were the moments? The one that first comes to mind is when Hoffman played Ethan Hunt.