Just saw Fallout. Really enjoyed it, it has all the usual strong points and the final sequence literally had my palms sweating. But this is pretty much the same film as the last three. As flawed as the second film is (though I still enjoy a lot about it), I kind of miss the days when the franchise was doing something wildly different with each installment, before JJ combined everything good about the first two movies and the tv show and filed off the rough edges.
It also runs a little long. That combined with the lack of surprises makes this an MI film I'm not likely to re-watch for a few years at least.
I enjoy all of the films to a similar enough level that it doesn't feel worthwhile my ranking them. 3 and 4 are probably my favourites, then 1, 5 and 6 jostle. 2 is last, BUT I still enjoy a lot about it.
However, I happen to know that @BigJKO just embarked on a franchise re-watch (only including 2 on my insistence!), so he may be able to give a more precise ranking at some point soon...