I went into this movie worried that this would be like the Transformers sequels with a ton of crap thrown on the screen with little to no substance. Thankfully I was wrong. The movie was very entertaining. Good but not too much action. Great banter between the characters. Good character development of the ones that don't have their stand alone franchises. And lots and lots of fun. I would only make two knocks against this one. First, a lot of the story was super rushed. As great as Ultron was, it was like you blinked and there he was hating the world. Second, there was some major lacking of continuity from Iron Man 3 to this movie. Tony Stark went from being done with being Iron Man and destroying all his robots to being with the Avengers and having newly developed robots.
Regardless of those two knocks, I would absolutely recommend people checking this out. It is a great summer popcorn movie. I would have it somewhere in the 4-6 range if ranking all the Marvel movies since Iron Man.