To start out right away, this movie was awesome. It surpasses batman begins, but to me felt very different from it mainly because begins was an origin story and this movie was a lot more about the joker and harvey dent. Some people may like the first one better, but the majority i think will like the dark knight better.
First off, the villain in this movie is much stronger than the one in batman begins (and ras al ghul was not a weak villain) and may be one of if not the best villain ever portrayed on screen. Ledger was brilliant as the joker. From his freaky outfit and scary smile, to his little mannerisms of smacking his lips and the way he walked, and to his voice which would range from high and weird to deep and terrifying in a few instances (One time he yells, "Look at me!" to a hostage he has in a video he made).
The joker doesnt want anything, whether money or power or fame, and this is what makes him such a good villain. He kills for fun and is a mass chaos causer. To put it in the words of alfred, "Some men just want to watch the world burn." The Joker really pushes batman and harvey and everyone in the city to the limit.
Also, Aaron Eckhart is very good as Harvey Dent. He is a district attorney that is not afraid and is the hero that gotham needs as he puts mob bosses behind bars. He is dating Rachel and is loved all around the city. The joker pushes him to h is limit as well, and he doesn't respond as well as batman. Eckhart does a good job of portraying him as one of the few good men in gotham city and his fall from grace at the end.
The second star of the show to me (with Ledger being the first) was director Christopher Nolan. He does an excellent job with the plot and with the terrific action scenes. The plot in this movie is more complex, and the movie has a series of climaxes that will keep you on the edge of your seat for the last hour or so. There are a lot of points where you expect certain things to happen, but something totally unexpected or surprising happens, with the joker causing most of the surprises.
The movie is really about how heros are so important to people. It shows how even the best of us can go bad. There is a strong theme of escalation in this movie as talked about in the end of batman begins. The evil and danger is much greater, so the heroes are pushed much harder.
Bale was very good in his role. He was excellent as Bruce wayne, with some funny jokes and good scenes with alfred and lucius fox. He was pretty good as batman, although his voice seemed extra deep and gruff the whole time.
All in all, this was a great movie where all the different parts worked together to give you a great story. Nolan's directing and writring alone make this a very good movie, and ledgers performance just makes it excellent and oscar worthy.