I saw "MISSION IMPOSSIBLE: Ghost Protocol" last week. It was a good movie and I enjoyed myself - with one exception. There were elements of the movie - events happened where I couldn't suspend my disbelief.
The gadgets? Yep. I believe that all of those amazing gizmos could and do exist - and are being used in the Special Ops field today.
Do I believe that Tom Cruise is 6 feet tall - or at least taller than all of the people around him? Sure. Why not? It's a movie. Go with it.
What I don't believe is that someone (Tom Cruise) can take a hard smack in the head and continue to function normally immediately afterwards. I don't know about you, but I got clobbered a couple of times in my misspent youth. I know from first-hand experience that after you've been hit, you're not seeing straight - let alone saving the world. Your only concern is "Which one of the three images in front of me is real?"
Tom Cruise get hit - and I mean CLOBBERED several times in MI:GP. Any one of those hits would have hospitalized a human being for days - yet, he took the licking and kept on ticking. That totally removed me from the story. The "Wait a Second...!" is all it takes to lose your audience.
In the 1988 movie, "U.S. Marshals" actor Joe Pantoliono's character was T-Boned in a car crash. The character was shown woozy throughout the rest of the movie. Not an ideal situation for a lead character - but perfect for a supporting role. It was 100% real and I loved it. Not only that - but it gave consequences to the rest of the action in the movie.
In CG Animation they deal with it, calling it "The Uncanny Valley" - where the animation design moves beyond cartoon style, becoming too realistic. This alienates the viewer - because the people just don't look or move properly - almost like zombies. This was best shown in the Robert Zemeckis film "The Polar Express".
So what's the point? Stylize it. For CG - 100% lifelike motion and design shouldn't be the goal. For live action - there should be consequences to action sequences. If there's a bone crunching accident, acknowledge the crunched bones.