Controversial, classic, and a reasonable sequel.
The Marvel series of films has, for the most part, been highly successful. The Avengers series has taken a group of comic book superheroes and created not only one successful franchise, but successful franchises for the individual members of the Avengers team (excluding Black Widow and Hawkeye who the studio have not felt fit to give them their own movies). This is the second of the Avengers films.
Iron Man, Captain America, Black Widow, Hawkeye and Thor are officially the Avengers team, battling bad guys around the world. During a mission fighting HYDRA in the fictional eastern bloc country of Sokovia, Tony Stark (Robert Downey Jr) AKA Iron Man has a spell placed on him by the Scarlett Witch, who with her brother Quicksilver, are fighting the Avengers.
Tony has a vision that the Avengers will be killed and he is responsible. With that vision firmly in his mind he wants to develop a self-aware super android who can replace the Avengers, and thus ensure Earth's safety. Sadly, like Dr Victor Frankenstein before him, his dream goes awry and Ultron turns out not to be Earth's saviour, but the vehicle of its destruction. Only the Avengers can defeat Ultron, but Ultron creates rifts in the team which might not be able to be healed.
I am not sure as to how true this story is to the comic books, but from my understanding the current line-up of Avengers is not the classic line up. With the introduction of new characters such as Vision and the Scarlett Witch, Avengers 2 is a return to the fundamental ‘historical’ avengers of the Comics. The whole film as more of a comic feel to it as well with the cinematography of the major fight sequences.
Wheldon has tried to right the imbalance with Hawkeye and Blackwidow by giving them a sizable part of the story over Thor and Captain America. I liked this and it fleshed out the two characters for me. Also it was clear that Whedon intended to kill Hawkeye as soon as you were introduced to his wife and family. Whedon was setting Hawkeye up like Goose from TopGun, who got cooked later on. How that plays was clever, but may leave hearts broken.
The script retains some of the humour from the first film to counter the drama. The moment between Captain America and Thor was very well done. James Spader as the voice of Ultron was cool, he was the perfect choice as the villain and despite being just a voice brought a nice presence to his scenes.
All in all the film was a good sequel, and set the ground work to continue the franchise(s) onward. However I am unsure what Avengers 3 will be about or look like. If there is a new set of Avengers I will not be as keen to see it. I am simply not invested in those characters.