When The Dark Knight came out, I bought the mp3 version of the one-disc score from Amazon. However, a short while ago it came to my attention that a 2 disc version of the score had been released. Oddly enough, the first disc was identical to the original release; the second disc had additional, unreleased music plus four "remixes". I absolutely had to have that additional music (except for the remixes; I hate remixes). Given the cost of the set (an outrageous $51.99) I was very grateful that Amazon allows you to buy individual tracks for $0.99. Thus, I spent an additional $10 and effectively ended up with the 2 disc score.
Although I enjoyed the Batman Begins score, The Dark Knight is substantially better. While it may not work as stand-alone music for some listeners (the music is closely tied to the tone and events in the movie), it is a fantastic work with a good balance of exciting, menacing, thoughtful, and tragic music.
The score is dominated by three musical cues: Batman's, the Joker's, and Harvey Dent's/Two-Face's. Batman's musical cue shows up from the first movie effectively unchanged. The Joker is given an atonal synthesizer score that is very appropriate for the portrayal of the character (throughout the movie I was able to predict when the Joker was about to appear since he is often preceded by his theme). Finally, Harvey Dent's/Two-Face's musical cue, like the character, depicts both dignity as well as tragedy.
My only complaint is that, like nearly all scores, the music is incomplete (about an hour or so of the music from the movie is missing). Nor is the music presented in the correct order. In fact, several individual tracks contain music from disparate parts of the movie. This is standard practice for movie scores, but it would have been nice to see The Dark Knight get the same treatment as Star Wars Episodes I, IV, V, and VI or the extended Lord of the Rings scores.
The music that's there is excellent, but the score's incompleteness and disorder earns the collection a 4 1/2 out of 5. By the way, if you intend to purchase the score, save yourself about $33 and buy the mp3 version of the collection.