Because, our school told us to watch the film and critique it as an example of good literature. As an English major, I felt like I was being slapped and spit in the face when I was reading that. Your teacher sounds like a hack. There are great film adaptations of books, sure, but then they become examples of good
cinema, not literature.
To answer your original question: "good" is, of course, subjective, and it's subjective to critical theory at the time. What really makes a text "good literature" is if enough reputable literary critics argue that the work is indeed laudable. This is done through essays that examine:
a) the complexity of the text (patterns, subtleties, craftsmanship, etc.)
b) both how the text reflects the tastes and sensibilities of its time and how the text influences future literary works.
c) how the text can be a continual source of research and discovery.
Critical theory and approach changes constantly, though, so works that were once considered "trashy" may be put on a pedestal in the next generation. For centuries,
King Lear was considered awful because of its unrelenting ending (a famous Victorian director even changed the ending so that Cordelia lives!), but today it's considered one of Shakespeare's greatest plays, and its ending one of the most potent in all the dramatic canon.
Personally, if you ask me what good literature is, I would say that a) it is something with underlying themes that are implicitly (rather than explicitly) stated, and b) that it offers itself up for study through the work's complexities and ambiguities.
BlueWizard's blog: The Rambling Corner
HEDWIG: "The road is my home. In reflecting upon the people whom I have come upon in my travels, I cannot help but think of the people who have come upon me."
