1. Old Man Hank Pym
2. Hope Van Dyne is the Wasp
As much as I liked Shaun of the Dead, it feels like a huge mistake to have sat on the characters of Hank and Janet because someone, someday, if he ever got around to it, wasn't going to make a movie about them anyway (and the script he turned over didn't have Janet in it at all, so it was a double waste that she didn't get to be in the Avengers movie, since he didn't have any plan on using her at all!).
Even if they'd been introduced in tiny sequences mid-battle-of-Manhattan, and Fury had responded to Iron Man asking about what he was seeing with 'You think you are the only remarkable people I know?' it would have set them up to appear for real in later films. (Hank could have appeared as a giant figure that sprang up next to one of the flying leviathans and wrestled it down to the ground, shrinking out of sight as fast as it happened, leading to Iron Man's outburst. Janet could have shown up when Hawkeye ran out of arrows, and said over comms he needed a fresh quiver, and a woman's voice replying that she's on it. Moments later, a tiny figure throws something at his feet which grows into a fresh quiver full of arrows, and she streaks off and takes out a Chitauri flying sled by zapping the pilot in the face. 30 seconds added to runtime, maybe, and they are ready to use in the next movie.)
5. Killing off Quicksilver in his first actual movie appearance
Yeah. Whedon likes his bait-and-switch's, and he was telegraphing hard that Hawkeye was going to die. (Which is traditionally what happens when a character who hasn't had a past suddenly starts talking about home and family and a farm and 'wanted to see Montana' and thinking about retirement.)
Instead, Quicksilver, who I found a much more comics-accurate version than the Fox time-manipulator version (who can *listen to music at normal speed while bullets stand still around him*), is the one to kind of undramatically die (so undramatically that Hawkeye pretty much jokes about it while lounging near the corpse).
I didn't like Age of Ultron for many reasons, but the pointless death of Quicksilver was near top of the list.
Other quibbles;
Chris Evans has been an unexpected but excellent Captain America. Robert Downey Jr. has redefined Tony Stark so much that comic-book Stark has been written to be more like him. Scarlet Johanssen is a great Black Widow, and I like her more than the comic book version. Mark Ruffalo is a great Hulk, and, more importantly, the most engaging version of Banner I've seen.
And then there's Chris Hemsworth. Big goofy smiling charming Australian surf-jock rom-com gleepy boyfriend material. *NOT* a thousand year old super-intimidating god of war and thunder that even Captain America and Nick Fury find impressive and commanding and a tiny bit scary. I've got nothing against Hemsworth, I think he'd blow Zac Efron away in the sort of movies that Zac Efron gets cast in, but he's no Thor. At least Thor: Ragnarok gave up on trying to walk away from his strengths and went full comedy with him.
And Jeremy Renner. I don't blame him for Hawkeye getting crappy lines and some crappy plotting (that results in his character being most effective when mind-controlled by Loki, for instance). I do blame him for making me regret that Quicksilver saved his life, since Quicksilver, in a third the time, was way more fun a character. Also, the man is a gaffe machine. Multiple times during the Age of Ultron cast appearances, he had to be apologized for, for saying stupid misogynistic crap about the women's salaries, or that the Black Widow was a giant **** for being teased at shipping with Cap (who she never slept with), his character (who she never slept with) and Banner (who, third time's the charm, she *still* never slept with). That's a pretty wild definition of '****' Jer... Does she need to wear a burka and never be seen without a male relative escorting her to avoid that label in your mind?
The decision to kill off the Maya character in Iron Man 3, and make Killian the 'big bad' was annoying to me, even more so if it's true that the decision was made because they didn't think toys of a female villain would sell. She invented Extremis, it's kind of foolish to think that a bullet from someone who was essentially her PR guy, would kill her.
Pretty much anything Drax said in Guardians of the Galaxy 2. Way, way over the top. Not funny to someone from my pre-Beavis and Butthead generation.
Louder does not necessarily mean 'funnier.' Not a big fan of Mantis, either. Would have much rather seen a new 'daughter of Thanos,' Moondragon, with psychic talents awakened by exposure to the Mind Stone (which A) we knew Thanos had before he loaned it to Loki, and B) we know can give select people super-powers, as it did with Wanda and Pietro). And halfway through an epic fight, we find out that she's the long-thought-dead daughter of Drax, because, it turns out, we'd already established in the first movie that Thanos likes to kill families and steal their little girls away to raise as his deadly daughters! That could have been a pretty epic 'family' subplot.
