I'm not a fan of horror or thriller. Nor am I much of a fan of horror soundtracks. But 28 Days Later..., film, soundtrack and all, just blew me away. The film itself is a mark of greatness; Danny Boyle has done an outstanding job, Alex Garland is a total genius and Cillian Murphy is as fit as ever, and as for music... John Murphy (et al) totally changed my opinion of film scores.
Like most horror film scores, the most tracks are typically rock based but with synths, vocals and virtual media (me thinks). The opening track stole a section of the film with random sounds from news programs, sirens and other random noises that all make up the rage theme. Enter the chilling synths, followed by what I guess is virtual media, with guitars pumping out power chords by the dozen to create the thrill. And you know what? It sounds *ace*! Everything fits into place, and if you've seen the film, you can just close your eyes and see it all again.
With additionals like Blue States, Grandaddy et al help to loosen the tense atomsphere and create a little fun in the music. Vocals such as Abide with Me create a sad, hopeless setting of sorrow and death, the words "Don't Wake Up" being replayed in your mind.
Having said all this, people do often say that seeing the film first helps. In many ways it does, but I still highly recommend it.