BTW, seeing this movie made me realize that I really wish that the Russo's had directed Age of Ultron.
I think Whedon nailed Avengers 1 as perfectly as anyone could be expected to. He captured and translated the light-hearted comic book feel to the screen perfectly and set the standard for which team-up movies with a shared universe are done. The "quips" thing was never really a truly valid criticism in my eyes, but Whedon's brand of humor and writing lent itself perfectly to telling the first Avengers story perfectly. I wouldn't even want the Russo's to do the first Avengers movie if I had the option.
Age of Ultron on the other hand.....well, it's a movie I think many people underrate, but nevertheless think is weaker than the original. Part of it is...*sigh*, yeah the non-stop stream of constant jokes could get grating with how irreverantly they treated the situation at times, but they never got in the way of the story being told. They just got in the way of it being told as well. AoU was trying to tell a more substantial story than the first avengers, and it just got very, very confused. Ultron was making the point that the Avengers were unworthy of being regarded as heroes and there is a lot of allusions to how each avenger considers themselves a monster or broken in some way, and them coming together to save Sokovia was meant to be them developing their characters but....well, it's just hard to parse that with the fact that what Ultron was saying was absolute gibberish. Ultron's psychologically is almost pure gibberish of why he thinks what he thinks about the avengers and the only thing you can say about him in the end is that he's crazy. Which undercuts what he says about the avengers, making them look silly for taking his inane criticisms to heart.
I wouldn't call Thanos the perfect villain, but working though his psychology makes much more sense as soon as you realize that you shouldn't take him at his word in regards to why he wants to kill half the life in the universe. His psychology makes perfect sense and it's satisfying to see it interact with the Avengers. I think the best way to describe it is that Thanos causes them to bring out their worst selves. Thanos turns the Hulk cowardly and weak, he reduces Thor to desperate rage, he breaks Iron Man's will...only cap manages to not compromise himself in the face of Thanos. Thanos doesn't do this on purpose, he doesn't explicitly prompt self examination the way Ultron does, but in terms of storytelling, the Russo's have a very clear, distinct idea of why Thanos does what he does, and how he changes the people around him. And this was shown in the Russo's other film as well, as you can very clearly map out how Tony breaks under the increasing guilt and stress that Civil War piles onto him.
So when I say that I wish the Russo's directed Age of Ultron, it's not because I think Whedon did a shit job or anything like that, but what he was attempting to do with Ultron didn't pan out because ultimately, Ultron was just insane and that was all there was to him. Trying to find a consistent motivation or philosophy is fruitless because it was always changing and shifting to whatever he needed at the moment to justify his homicidal tendencies. Under the Russo's, Ultron's "You don't want peace, you just want quiet" may have had some actual weight to it.