Dear Mr. Whedon,
Thank you, thank you for the Avengers movie. And thank you for doing everything right. There are so many ways this movie could've been screwed up, and you did none of them.
You could have unbalanced the cast. I mean, shoot, there were like seven heroes, five of whom have (or deserve) their own movies. By all normal screenplay calculations, the cast should have been unbalanced! Ironman should've stolen the show, or Thor should've been relegated to some kind of adviser role, or at the VERY LEAST Black Widow and Hawkeye should've been ignored entirely (I would even forgive you for that last one).
But they weren't! Everyone had their moments. Every character was believably, realistically involved. Thor and Loki had brother issues. Black Widow and Hawkeye had a freaking non-romantic relationship. Captain America was still dealing with the fallout from his last movie (heck, they all were). I love them all!
You could have revealed something lame that demeaned or flat out broke the original movies. You wouldn't have been the first. I mean, how do you explain why there are billionaires and WW2 super soldiers fighting alongside gods? To save the planet from alien invasion?
Dang, man, you actually made the prequels better at some points. The Thor movie didn't make me stand up and cheer, but you made Thor and Loki's characters deeper. You gave Captain America a reason for his ridiculously patriotic uniform. Thor quipped about how Asgardians always seem to beat each other up when they come to Earth (even though they're supposed to be more civilized).
You took the holes in the character's backstories and said, "Ha! Hey guys, look! A hole!" and then moved on. I love you for that.
And yet, in this movie, Natasha acted sexy or weak only twice, and both times she was totally messing with someone to get what she needed. So. Awesome.
You could have written cheesy, cliche dialog. I mean you couldn't have, Joss, because you're not like that. But Hollywood could've put someone in there who left the "This is just like Budapest" line as is, or who didn't understand how Tony Stark's ultra-clever Disregard for Everything works.
You could have made the Hulk into a dumb tank. It would've worked. I mean, that's what he is. And you did make him into a tank, but a super awesome one.
We didn't even see the big guy until halfway through the film, but two minutes into Mark Ruffalo's first scene (who, by the way, I might have to write another love letter to; he is now my favorite Bruce Banner of all time) you made sure we knew how scary the Hulk is. Not by telling us, not even with dialog, but by showing it on Black Widow's face when she was too afraid to put her gun down.
You could have done any of this. It's what's Hollywood has done with most superhero movies. And I forgive them, because the stories are fun and the heroes are awesome. But you? You made me fall in love with Thor and Hawkeye, characters I used to make fun of.
You have already had a significant influence over the novel that got me an agent. But now I'm going to watch everything of yours I can get my hands on. Thank you for influencing everything.