So I picked a sleepy Monday night, well after the movie's release date to check out my first summer blockbuster. I'm too old to fight with crowds. I think there were fewer than a dozen other people in the large theatre. I did not spring for the 3-D version, and by all accounts I didn't miss much.
Bottom line: I had a lot of fun. I read about the Avengers' nemesis Ultron back in early 70's, back when I could free-ride off a fellow college student's comic-collecting mania. In addition to the superheros from previous installments, we get the Vision, Scarlet Witch, and Quicksilver here. Cool!
I should talk some about the plot: the Avengers are sent to assault the last Hydra stronghold in some fictional dinky European country in order to recover Loki's scepter, somehow misplaced in an earlier movie. They do, but the "magic" in the scepter is actually technological mumbo-jumbo that Tony Stark feels he can use to defend the Earth against the hostile alien menace that he (correctly) thinks is about to attack.
Stark's high on hubris, and this time it bites him in the ass. What he creates is not the obedient robot he expected, but one who concludes the most direct route to peace is to eliminate the obvious troublemakers: i.e. the entire human race.
There's a lot of frenetic battle, but each member of the team gets a chance to shine, playing a pivotal role in their (oops, spoilers) eventual victory over Ultron. Everyone's brave, and despite occasional violent disagreements, the team eventually peforms brilliantly.
If I had a quibble: things are often way too frenetic, in the sense that you can't quite tell what's going on: everything's a fast-moving blur.