It's one of my weird quirks as a film critic: I'm compelled to read source material beforehand if I can. And no question, sometimes it can be a huge mistake. ---

The new Oliver Stone film Savages opens July 6, based on the novel by Don Winslow. It tells the story of a pair of California pot dealers who get entangled with a Mexican cartel, with increasingly violent consequences. Without offering any specific spoilers, suffice it to say that the ending of Stone's film takes liberties with an ending in the book that seems almost essential to the story's thematic and moral content. Plenty of notable changes were also made to this summer's film version of the musical Rock of Ages, all of which also seemed intended to address worries that audiences don't like downbeat finales.

These were only two of many examples from my movie-going life where familiarity with the book/play/true story has provided a jarring contrast with what the film version offered. The purpose behind my personal philosophy of being familiar with the source material is understanding that plenty of people come to movies with that baggage, whether the book is a best-seller or an obscure oddity. Occasionally, you can actually see an improvement; often, it's obvious why a certain change needed to be made for dramatic efficiency. And plenty of times, you just want to yell out loud, "That's not right!"

What have been your most memorable "the movie screwed up the source material" moments? Have there been times when you actually thought a movie made improvements on the material it was based on? And how much should we expect movies to stick to the source?