These do seem to get more 'grandiose' with each part, which tricks people into thinking they're better, but even through they're all good and very entertaining, upon rewatching all over the years, I'm sticking to the order of release as to the ranking.
I do like M:i-2 a lot, and think the story in M:i-3 is probably the most interesting, with the best cast of all (Philip Seymour Hoffman, Michelle Monaghan, Maggie Q, Fishburne), but the first film is still the most 'Mission Impossible'.