I just finished watching it and i must say that the late PSH has done a pretty good job in his role as the villain. He was cold, calculated and charismatic (especially with the opening scene). In this movie the pacing and action are handled pretty well, the plot and story is plausible and you care about Ethan's relationship and it has also a good cast overall. I'd say that it's easily the best from the original trilogy and a solid 7.5/10 for me. JJ get criticized for his last star wars movies but i think in this movie we can clearly see that he's pretty good at handling simple characters and at directing action scenes.
In conclusion: M:I:III is an enjoyable action flick, worth the 2h run, filled with twists and nice action scenes and it's when the saga started to be more about action then spy.