Considering that this movie broke the record for opening weekend box office gross, you probably don't need me to tell you to see it. Still, I figure I should tell you what I liked about it in as spoiler-free a manner as possible.
First, I liked this movie's take on the Joker. A whole lot of people have talked about how this Joker is the ultimate force of chaos. That he is an anarchist with no fear because he has nothing that wants other than to "watch it all burn". This is all true, but it doesn't get at the heart of why I liked him.
I liked him because of the sadistic social experiments he performs throughout the movie. Throughout the movie Batman is stymied in figuring out what the Joker wants, but what the Joker wants is obvious. The Joker wants to prove that when it comes down to it, everyone is as bad as he is. That civilization is a thin veneer which can easily be peeled away with just the slightest amount of pressure.
The Joker would have no problem killing your mother or your wife in front of your eyes, but given the choice he would rather get you to do the deed. Especially if you had to choose between them. Especially if the game was rigged so that you would lose everything anyway after you made your choice.
To quote Alan Moore from The Killing Joke, the Joker believes that the only difference between you and him "is one bad day".
Aaron Eckhart's performance as Harvey Dent was also a lot of fun. While most of the press is justifiably talking about Heath Ledger's scene stealing performance as the Joker, Harvey Dent's character is the most dynamic in the movie. The Joker is less a person then a force of nature. Harvey Dent is a man who finds himself having to cross lines he never thought he would cross. The Joker has nothing to lose, while Harvey Dent loses more than he though possible. Aaron Eckhart takes us through this character arc so effortlessly that it is easy to overlook how good his performance is.
Of course, Harvey Dent's journey is just a dramatic echo for the journey Batman undertakes. There is a thin line that separates Batman from the villains he fights. At many points in the movie he walks right up to that line. In some cases, he crosses it. Despite all of this, his "victory" is pyrrhic at best. This is the movie where Batman loses.
So if you think this would be a movie you would enjoy at all, I would recommend that you see it. Its not "just" a good comic book movie. It's a good movie.