Spoiling the Ending

Aristotle discusses in his Poetics, what he thought were the essential elements of good drama: true to life plots, reversals of fortune, flawed characters etc...but the idea of a plot twist or surprise ending was unknown to him. Is this an important element of plot that he hadn't considered?

I think that perhaps it's an aspect of drama that if used correctly, can add dimension to a story, but it's not essential. Thinking about recent films, in "brain in a vat" type movies like the matrix, we are able to relate to the main character more because we experience the same "Anagnorisis" that the main character experiences as the truth about reality is gradually revealed. This also works well in crime mystery type films because it allows us to better understand the thought processes of the investigator. However, in most of M. Night Shamalon's films, it is used more as a gimmick: the plots are often purposely vague and confusing, in preparation for the big surprise at the end. In these cases, I think it would be better to stick to the essentials that Aristotle mentions.