Kevin Feige is the baddest dude in the movie industry.
Joss Whedon is also pretty badd.
The moment I knew they had pulled this off was when the Helicarrier lifted off and we walked onto the bridge. Nothing else has yet felt like stepping so completely into the world of Marvel comics.
I really love things about Iron Man 2 and Captain America, but those films have problems, especially in the third acts, that make them feel painfully botched, considering that there's probably no do-over. The Steve Rogers hour of Cap is good; once he fully becomes Captain America, the movie largely stops working. Iron Man 2 is fun, it's hilarious, the Monaco scene is great. The fight at the Stark Expo doesn't work. There's probably no second shot at a period Cap film. I don't know if there's a second shot at an Iron Man/War Machine "buddy" action film (which is what I'd really hoped IM2 would be, and which it managed to be for about 90 fun seconds towards the end.) Avengers tries something more complex and ambitious than either of those films and it works.
This is not just the culmination of Marvel's output until now, this is the new standard and the beginning of their future. They've got license to start going crazy. "Cautiously crazy," I'd expect, knowing them, but Thanos is a promise that crazy things are coming. Their next "solo" films still have to work. They can't afford more as dysfunctional as Cap and IM2 and they definitely can't afford to do worse than that. If you watch their progression, though, from 2008 to 2010 to 2011 to 2012, they seem to get closer each year to figuring out exactly what they want to be doing as a studio. It shows.
After this, I totally believe they could throw Beta Ray Bill into a Thor sequel and make it work. I believe they can make that Guardians movie with Groot and Rocket Raccoon. You're gonna see Black Bolt. Dr. Strange can meet Eternity and the other huge, "abstract" entities. A lot of this might be on the other side of Avengers 2, but this is where they're heading. I never thought anyone would be able to do this.