A while back I posted a couple of links to some articles written by Matt Fudge over at the Ikonograph blog analyzing the worldview of the recent Dark Knight movie (found here http://theimageiseverything.wordpress.com/2008/08/03/heath-ledgers-joker-crazy-like-a-fox/ and here http://theimageiseverything.wordpress.com/2008/08/08/sweet-eureka-the-ironically-dark-knight/.) They are very insightful.
However, I would also point you to a recent post by Matt Kaufman over at the Boundless blog where he also discusses the new Dark Knight movie and deals with the issue of whether or not Christians should watch movies/television which is so dark. It is well-thought out and worth your time to read. You can find it here http://www.boundless.org/2005/articles/a0001824.cfm .