I saw M:I:III on opening day. It was much as Ebert had said it would be - 2 hours of non-stop action. Is that good, eh, is that bad, eh. I'm a fan of the action flick, however Mission Impossible is not supposed to be an action series, it's supposed to be intelligent film/television. The first Mission Impossible movie was not bad, there was some thinking involved, and required. The second film pretty much abandoned plot, and in its third iteration, the plot is completely a by product something to fill the 2-3 minute segments between action sequences.
There were several times in the movie that I literally laughed out loud at the "drama" unfolding before me. That's not to say it wasn't dramatic, it was, my problem was that I wasn't as tied up in the moment as the film makers might have liked. It was obvious what the outcome of this dramatic moment must be in order for the film to continue, and the inevitable ending to come to be. There was one plot twist that I was angry at myself for not catching, however for now I'm going to say that was one there weren't any clues to, other than simply a Maverick style plot twist, but I'll have to watch the film again to see if there were any clues I missed.
Bottom line - Great action, get lost in the action and don't look to far beyond the current moment, otherwise it will be entirely too predictable.