The soundtrack is amazing with a lot of classical music underlining the scenes in a perfect way. Kubrick was a perfectionist and that extended to the songs he used in his films, and also to the great use of shot selection and lenses etc that are also obviously on display in this wonderful film.
The story is engrossing and seems much shorter than the actual run time of the film which is about three hours.
The effects were amazing and even after all these years they still hold up as being really good. Some of the lights-flashing special effects scenes come off as a little dated but considering how old this movie is they did a really amazing job.
And the ending is one of the best you will ever see, it is open to interpretation and brilliant!