1-Very serious themes: the MI have never dealt with a threat that feels so serious and personal to the audience. They want the movie to be taken seriously, and to raise question about AI, audiences want great entertainement. They kind of now that, and whereas the chase in Paris was very serious, the one in Rome has a lot of fun, but it doesn't really work. You can't compensate, as shown by the Pierce Brosnan's Bond which also tried.
2-Have it be a Part 1: the end is therefore less emotional and can't compensate for the issue I'll raise in 4-
3-A different pacing: the three acts structure of Fallout and Maverick was perfect, here they want to have more. A much longer cold opening, which ends up being too long, and leads to a less well paced movie. We even cut away from a big setpiece before the end (airport running).
4-The end of scenes is just not satisfying: at the end of the chase in Paris, Cruise gets Lane. It's thrilling and we get to point B. In London he loses Lark but it leads directly to Act 3. Here, he never gets Grace, she keeps escaping. Making the end of the chase in Rome less satisfying: no evolution of Grace as a character, Hunt not much closer from his goal. And in Venice, when Grace grows as a character, it's overshadowed by the decision which in my mind mostly makes the film a failure at the Box-office (with its release date
): the death of Ilsa Faust. It's the first time the franchise kills such an important character. Never had the franchise killed one of the main character
from another movie. And she dies, and it's not even in the final act of the film! If it was to give a bittersweet ending like Skyfall or OHMSS, why not? But here ? It really betrays the love the audience has for one the best character of the franchise.
5-The film has a difficulty making Luther, Ilsa and Benji participate in the action. The joy of those films was the group, it's much less present here than in 4, 5&6.
In the end, despite being one of the best script of the franchise with MI1&5, one of the most interesting thematically with MI1, and having incredible stunts that rival 4&6, the film is the least satisfying of the good MI (meaning I leave out 2&3, which are weaker films). it's a very well-made film but just not one that leaves you as entertained or exhilarated as 4, 5 & 6. And not as well mastered in what it says as 1. (I mean, De Palma was cooking). It's very interesting because it's such a well done film, what a score, the photography is beautiful, but it doesn't work as well as the others.
5>6=1>4=7