At two hours and 43 minutes, this really could have used some tightening up. The gunfights, fistfights, knife fights, chase scenes, etc. just seem to go on and on. And there's a lot of Tom Cruise running. Impressive endurance and speed for a guy his age, but …
Guilty confession: it took me three tries to watch this all the way through; I kept falling asleep. I assume (like Top Gun Maverick) that it would have been better to watch in a movie theater, but I just didn't make it.
The plot seems to be an afterthought, not particularly coherent, just an excuse for all the running around, but as I understand it: there's an evil sentient AI afoot, dubbed the "Entity". The opening scene has it compelling a Russian submarine to (essentially) commit suicide. There's a key involved, which has two parts that must be fitted together. It does something important, something to do with "source code", but the Entity seems to operate just fine without the key in the ignition. The Entity has a human accomplice, Gabriel, who, years back, killed a lady Ethan Hunt was fond of. Captain America's girlfriend, Hayley Atwell, manages to snag one part of the key, which gets her involved. Two blond ladies of dubious morals. A desert shootout. A traitorous higher-up, see if you can pick him, or her, out.
All of that's fine, but I kind of miss the somewhat more laid-back TV show.
Another gripe: long, intense scenes where a group of people sit around and do plot exposition, each actor dropping a line in turn about what has happened, or needs to happen next. You get the feeling everyone's telling everyone else what they already know.
And yet, sure, I'm on board for Part Two. Probably in the theater.