The actual soundtrack, not the extended version that includes numerous compositions by Wendy/Walter Carlos that were not used in the actual movie (but still fit in very well, after seeing her explain them in the doc on the The Shining disc).
I think I could do a reading of the movie with a focus on soundtrack. I mean, before the soundtrack was just a great component of a great movie, but listening to the soundtrack itself, and hearing Carlos go into a bit of detail on the compositions, and the process of selecting which compositions would and would not be used, there's clearly a bit more to things than I originally thought. I am sure that many directors are very involved and invested in this process, but it's also evident that many great directors don't particularly care about their soundtracks. A recent example would be last night's viewing of The Departed, an entertaining movie with a ho-hum selection of tracks.
What stands out about the A Clockwork Orange soundtrack is that there are basically three types of songs on the album. There are the songs that are completely, obviously synthesized, using all the tricks available in the technology of the day in order to create a sort of "this is how music will sound in the future" effect (like, say, the movie's main theme and the take on the William Tell Overture used in the trailer). There are the standard classical compositions that use pretty normal sounding instrumentation (note: some of these also use synthesizers, but not to obvious effect; it would take a discriminating listener to tell). There are also compositions that carefully merge the other two types of songs--relatively straightforward takes of classical songs that use both normal instrumentation and obvious synthesizers (most notably, a few Beethoven tracks do this, although there are at least an equal number of "normal" ones).
Once it becomes clear that there are three distinct types of song used in the movie's soundtrack, it simply becomes a question of piecing things together and coming up with a supportable reading. I have not explicitly done a viewing of the movie while specifically watching for this, but thanks to the effect of music on the memory, I can picture at least a few examples, and come up with a potentially valid interpretation.
The all synthesizer music is used for things that are "alien" to the viewer. The main theme is synthesized (although there is later an orchestrated version of it), which helps along with producing the atmosphere of a strange future. Some elements of Alex's early movie bad behavior are also accompanied by the synthesized music. With the exception of one scene (the early droog fight), I think the synthesized music is a clear indicator of Alex being weird and coldly disconnected.
The normally composed music, I believe, is used as a sort of indicator of truth, beauty, or clarity. Compared to the other two categories, there are fewer of the normal tracks, and I think they tend to pop up specifically when, say, Alex is talking about Beethoven, the one thing he will admit to loving.
The mixed music, which tends to sound even more alien than the synthesizer music due to it mixing the familiar with the strange (along with atonal vocals in at least two of the pieces in this category), seem to be tied to the conditioning process and Alex's post-conditioning adventures. The combination of the normally composed music and the alien synthesizer music might be seen as Alex's alienation from his own world, aka Alex's one source of beauty and truth becoming corrupted by the strangeness that the viewer has been aware of all along.
Like I said, I'd need to do another viewing before saying anything conclusive, and I am aware of, offhand, at least two exceptions to the use of music, so I have to work those instances into the interpretation.
Still, it's pretty neat, how even the music can be seen as adding significantly to the movie. I believe I said 2001 had the best soundtrack of the Kubrick movies, but now I am not so sure. 2001 and The Shining have great soundtracks, but I would be hard pressed to come up with anything like this for them, which makes me think A Clockwork Orange has the best, since it can be seen as elevating the themes presented in the movie.