Two criticisms, both from a fan of the TV show:
1) You CANNOT reboot a old TV show, and then take the leader and hero and make him the bad guy. (It is like making Hanibal the bad guy in The A-Team) They did this in the first movie. Although to his credit, Peter Graves refused to be part of the first movie that did this, they still used the same character, but played by Jon Voight and made him the bad guy.
2) Much of the original tv show had the MI team doing their job without the bad guys ever knowing the team was involved. The first movie did not do this and after complaints it became a bigger part of the plots of the sequels.
Other than these two complaints, the movies are good and a lot of fun.