I knew this one was going to get the double thumbs-up from the first scene onward; as with pretty much every other decent superhero movie that's been made so far, this one worked because Joss Whedon stuck to the core character (and situational) concepts and did not let the story get diluted with nitwit second-echelon producer ideas about how to "improve the script". *COUGH* Tim Burton *COUGH*
With regard to the casts' performances, I'm going to have to cut out the middleman and just state that I think everybody did an absolute bang-up job. Two of my favourite scenes were when Loki and Natasha were doing their little intellectual tennis game with the backspins, feints and so forth, and the Black Widow/Hawkeye scrap. Call me the old sentimental type, but Phil Coulson's death did tick me off; that scene were he turns into a ten-year old kid around Steve Rogers, hoping for the trading-card autographs, pointed out that this guy definitely did have a life outside of work. And, yes, I was thinking, on many occasions, how this movie would have been made to fit into a V&V system scenario.
I did stick around for the Thanos cameo scene, but figured that was it and didn't see the last-last scene with the shwarma place. Needless to say, I am going to be seeing this sucker again and will make sure that I catch that one "live", as it were.
On a final note, the best comparison I can make, in terms of movie-going experiences, is with when Aliens first came out back in '86. One reviewer stated that it - Aliens - was a two and a half hour movie that seemed like it was an hour and a half: things moved that quickly and had that little dead space between scenes. Avengers gets the same kudos in my book - this is a rare event that will echo in the superhero communities - print and film alike - for a very long time to come.