"A lot of people are dead, Agent Hill. Somebody has to answer for that."
This… is how it could have happened.
Movies like The Avengers are just thrown together overnight. They take countless thousands of hours of planning and testing to make it to the big screen. Sometimes the plans don't quite come together, and you wind up with a deleted scene like this one – courtesy of Yahoo – which would have dramatically changed the tone of the Marvel Studios blockbuster at the very start of the movie.
In this sequence, Agent Maria Hill (Cobie Smulders) undergoes interrogation to determine "what went wrong" during the climax of the film. If you've actually seen The Avengers, you know that the finished film neither begins or ends on such a melancholy note, and that the heroes are significantly more victorious than this sequence makes them appear. The other big difference is the introduction to Maria Hill, which casts her in a more suspicious light from the get-go, and would likely have given her occasionally doubtful character a greater significance in the overall film. We'd certainly have been paying closer attention to her, since it appears for all the world that she regrets the entire sequence of events that brought her to this moment and openly disparages both her commanding officer, Nick Fury, and The Avengers themselves.
Of course, this is Joss Whedon we're talking about, and he's not one to write a scene like this without twisting it somehow. We'd be surprised if there wasn't also an alternate ending which reveals it was all part of a devious Nick Fury plan. Hopefully we'll find out when The Avengers premieres on DVD and Blu-ray on September 25, and we can take a closer look at all the excised footage.