The Superhero Registration Act is only referenced, but they explore how the government is uneasy about superheroes running around unsanctioned, and we see Rogers and Stark being placed on opposite sides of the conflict, with Stark believing in some sort of registration of the gifted, and Rogers being against it.
The Avengers are outlawed by the government. Stark retires, Thor goes back to Asgard and Banner has to get off the grid again. Captain America refuses to leave the world unprotected and reassembles with Black Widow, Hawkeye, Falcon, Quicksilver and Scarlet Witch.
That's a flashback of before they get their powers.
Only once, before Ultron disables all Starktech. Falcon is running down a lead on Bucky's whereabouts.
The Hulk out of control, killing everyone. Banner has been having trouble controlling the Hulk throughout the movie.
Asgard falling.
Thor creates lightning, the others storm the base and fight some mooks before Cap goes off to search the computers, the Iron Men go retrieve the stolen Chitauri technology, Black Widow steals data on HYDRA's research, Hawkeye and Thor fight some mooks alongside the Hulk. The Twins get released and there's a big fight, before they are defeated and captured.
Wanda rearranges his components to make him vulnerable to an attack by Hawkeye.
They find out Ultron is planning to extinguish the human race, murdering thousands of innocents.
Hawkeye is actually pretty good. He's instrumental to the Twins switching sides, he delivers some cool lines, and he delivers the killing blow on Ultron.
Strucker is just an opening villain. He has 10 minutes screentime, tops.
Serkis is Ulysses Klaw, a Vibranium scavenger who collaborates with Ultron to locate a large underground mine in Sokovia.
Claudia Kim is playing a scientist from a South Korean tech company and an old friend of Stark with some doubts about the Ultron program. Ultron attacks her company to steal some data and upgrade himself, leading to one of the movie's five big action setpieces.
Nobody dies. Hawkeye was going to, but not anymore.
Black Widow doesn't lift the hammer.
It's the Vision.
No Time Gem retcon. No gems in AoU at all.