For the reader's convenience I have linked to my previous reviews of the following movies: Iron Man, Iron Man 2, Thor, and Captain America. I don't think I ever wrote a review of the Edward Norton "Hulk" movie (I only saw it on video), which was far and away the best of the Avenger-team-member movies; a moot point considering that Norton got replaced by Mark Ruffalo for the ensemble movie just released. I mention the previous movie reviews merely to point out how exceedingly low my expectations for "The Avengers" was, just less than 24 hours ago. Some may laugh at this, but I consider myself a undying optimist when it comes to movies; no matter how critical I may be I'm always hoping for the best.
Jess and I have watched the "Firefly" show a couple times (it was only one season long). Joss Whedon created "Firefly" and wrote and directed many of the episode too. What Whedon brings as a writer and director to "The Avengers" is an understanding that good, funny characters are far more interesting than mindless action. He has taken three bland and one funny (but not two hours funny) superheroes, given them good lines, just the right amount of tension and created a movie which is actually entertaining all the way through. I noted in my review of the original "Iron Man" that I enjoyed the final fight sequence because I got a little nap in... This is the negative side effect of computer animation; "spectacular" has become boring. Whedon came close to putting me to sleep a few times; I actually dread the finales in movies like this, but he was smart enough to cut between the different heroes focusing more on the humorous interactions, and not putting too much emphasis on the action.
While I wouldn't go so far as to say that "The Avengers" atones for the sins of its predecessors; it does have personality, and personality goes a long way.