Sad I didn't see this thread as it happened, as I just rewatched them all (with my wife, who had never seen any).
Mission Impossible is a mess in certain respects (the cut content really hurts it) but probably the most beautiful visually of the entire series. De Palma was really putting in work. The Langley scene is obviously a masterpiece.
Mission Impossible 2 is maligned for no reason. IMO it's late Hollywood mania is perfect for the series. John Woo was trying to destroy the series and rebuild it from the ground up. I get why people didn't like it, but you can watch the latest Fast and Furious movies and they totally owe a lot to this. The Chimera plot isn't perfect (though I assume the rumored 3 hour cut would expand a lot on it) but it's one of the only coherent villain plots in the entire series. I mean, we all love Phillip Seymour Hoffman, but his motivations are a lot less clear at the end of the day.
Mission Impossible 3 is the first time the series feels truly "dark". I do like the setpieces (the Chesapeake Bay Bridge Tunnel sequence in particular) but the constant turns and twists don't really work, and the ending feels very flat. As much as I love PSH as Owen Davian, he really doesn't get as much screentime as he should. He's a great villain and all but I think maybe this movie is a tad overrated because of the fact that he's one of the only good villains in the franchise.