Good article, but there are a few points about Ultron you missed that make it an even more underrated experience:
Firstly, the film accomplishes/sets up/introduces so much and speaks to the volume of Whedon's talent that it wasn't a total studio-driven disaster.
Secondly, it's a lot darker than the first with the focus being on the Avengers demons.
And third, it explores is the characters deeper with flashbacks and flaws introducing their inner turmoil.
Where it trips up and where all of the above tend to be undermined is because at the halfway mark the film starts to fall apart and loses focus. Up to that point though it was pretty decent, if not really good. I think it gets overshadowed or pigeonholed as one of the worst because it failed to live up to the excellence of the trailer and turned into less of a Dark Knight and more of a Dark Knight Rises :S