Marvel has proven over and over that they really don't care about quality films - they exist mostly to advertise the next movie. They all tell pretty much the same story, and they're mostly crap. The same is true of "Avengers: Age of Ultron."
If you haven't seen this movie yet, there are spoilers.
And a caveat: I have never read the comics, so I have no opinion on how the movie compares to the comics. My thoughts are on this movie only.
1. By now, The Avengers (and their technology) are so overpowered that they're basically magical. They need to stop being superheroes and just go teach at Hogwarts.
2. The character of Ultron is a complete mess. He's an alien AI that wakes up, absorbs the internet, and then thinks he's God (but not only God - he's specifically the Christian God). After soaking in all human knowledge, he looks around, and thinks that the most logical way to bring peace to earth is to kill everybody. But he also gets scared and mad and has temper tantrums like a kindergartener.
Oh, and he looks like a rejected design for The Terminator.
3. While we're on the topic of Ultron, I have to point out that the idea of an AI that tries to become God has been used for decades. It goes back at least to the 1984 classic novel Neuromancer, which changed science fiction forever. Even Johnny Depp's AI in 2014's Transcendence was better than this lame metal ego. And when Vision stops him by grabbing his head and basically taking away his wi-fi connection, you know you have a bad villain.
I think Ultron's name should be changed to Leastron.
But I do like Samuel L. Jackson's nickname for him, "the platinum bastard."
4. The movie tries to be deep, but if you listen to what's said, it's just funny. Ultron says that we create what we dread: men of peace create engines of war, and parents create children. I was so caught off-guard by the apparent dreadfulness of parenthood that I didn't wonder until later, if men of peace create engines of war, do men of war create engines of peace? Is that what Ultron was getting at?
Later, Vision says stuff like "things aren't beautiful because they last" and "humans think order and chaos are opposites" and other pseudo-Buddhist quotes that are only impressive if you're a stoned 15-year-old.
5. When Hulk smashes a city, and the whole world is looking for the Hulk for possible arrest, the Avengers decide to avoid any consequences and go into hiding. And out of all the places on Earth they could hide from danger, Hawkeye takes them to meet his wife and kids. Then Hawkeye's wife lectures him by saying that she supports his "avenging" but... she's pregnant and family is important too.
6. The movie is sexist. One theme of the movie is the "deep" question of what could turn a human into a monster. Black Widow thinks she might be a monster because she can't have kids.
And while all the men are wearing suits that cover their skin up to their neck, nobody mentions to either of the two women in the movie that their suits were always open enough to show their boobs.
Oh, and their names are Black Widow - she wears a dominatrix outfit, and Scarlet Witch - she takes care of the schoolgirl fetish. A spider that kills males after sex and a bloody witch. People at Marvel have obvious issues with females.
7. The only way you get any "deep" character development is when they have visions about their past or future, caused by a spiteful Russian lady. And then Thor visits a cave to talk to the water spirits, to get another vision.
8. Ultron could have destroyed the earth by, say, covering the earth in chemical weapons, or swarms of nanobots, or lots of other things that would have overwhelmed the Avengers and prevented them saving the planet. But Ultron, in his infinite wisdom, decides to lift a city up in the air, and then drop it. You know, so the Avengers can all get together in one place and stop him.
At about this time in the movie, Hawkeye tells another character, "The city is flying. We're fighting an army of robots. I have a bow and arrow. None of this makes sense." I bet that was going to be the original title of the movie, but it was too long.
9. I get that this is a superhero movie, and it's not supposed to be deep or meaningful. But this is ridiculous.
In its favor, this movie is interesting visually. If that's all you need from a movie, then this movie is great.
This movie is basically like the people I used to date - attractive on the outside, but ugly and stupid and shallow on the inside.