The action in The Dark Knight is outstanding, as expected. You will be gripping the arm of your seat (or neighbor) during much of the movie. But the best part of this movie is the interaction between Batman and The Joker. Heath Ledger is excellent and creepy. There are a couple of scenes with him and Christian Bale which are the heart and soul of the movie. It may not be the best movie ever made, but it is WELL worth the price of the ticket. Oh, and don't bother getting popcorn, you'll forget it's in your hands as the action ramps up.
We took my 10 year old son, 8 year old daughter & 6 year old daughter. Girls loved it, son thought it was "pretty good for a movie about a girl". It was entertaining enough for parents to be engaged. Cute story, some stretches on the plot but nothing offensive for the kids.