The Avengers - It's not a flawless movie, but the single flaw (that every single piece of action feels hopelessly contrived) can be very easily forgiven and overlooked.
Iron Man 3 - I had never seen an MCU movie (I had seen part of Thor on a plane trip, and paid no attention to IM1 at a friends house, but that doesn't really count) before a hot day last summer when I decided to see this, I absolutely loved it, and it turned me on to the entire superhero comic genre thanks to the strength of both it and The Avengers. I can definitely relate to anyone who didn't like the Mandarin thing (ask me how I feel about Star Trek Into Darkness), but the action and comedy worked well with the story.
Captain America: The Winter Soldier - I felt Star Trek Into Darkness had the potential for a great action movie that was stifled by Damon Lindelof. Captain America is that great action movie - it has pretty much the exact same plot, except for the baffling addition of the wisecracking black guy, and it's really fun to watch.
Iron Man - Despite what Bob said, I feel Jeff Bridges added a lot to the movie, and actually succeeded in making it something other than RDJ The Motion Picture. He really propelled the movie into the annals of pop culture, though.
Captain America: The First Avenger - Yeah, I guess I kinda liked it.
Thor: The Dark World - I appear to be one of the few people who didn't mind how little screen time Malekith got. Yeah, we don't get much about him, but the movie is so crammed full of pretty entertaining weird crap that more would have been unnecessary.
Iron Man 2 - While I was saying that I had never seen an MCU movie before Iron Man 3, I remembered that - this is not a joke - I had taken some friends to see Iron Man 2, in the theater. I didn't remember a single second of the movie, and even now I can only remember something about the World's Fairgrounds from Men in Black.
Thor - Just the worst movie that I've seen so far. Loki's fine, and Chris Hemsworth is okay, but Natalie Portman is just boring, Asgard is badly designed and so much of the movie is just long stretches of nothing's going on.
The Incredible Hulk - Gets the bottom spot because I never felt the need to see it.