When the show's creators went forwards with this, they changed a lot of the conventional aspects of sci-fi TV - They rooted it in more realism, from set design, uniforms, situations and dialog, making it a very accurate show, at least militarily. One of the big things that was also a big change was the music.
A number of science fiction television shows and films have a very bombastic type of score - lots of brass, loud, dramatic and exciting. Just listen to the opening credits of Star Wars or the original Battlestar theme (which they actually brought back in Season 2 for one episode).
These soundtracks, like the rest of the show, is a bit of a reinvention. Like the show, the score here is darker and moodier. Furthermore, they branch out with their sound, utilizing a number of world influences from India to Ireland, giving this show a very unique sound.
The third season soundtrack is possibly the best of the three soundtracks. It compounds on a number of themes that have been introduced already in the series, and adds in some new ones. The album opens with a bang, with the first couple of songs. The music here is more dramatic, darker and richer in sound. It also includes the fantastic cover of Bob Dylan's song, All Along the Watchtower, vocals by the band BT4. It's a fantastic blend of the soundtrack's usual sound and rock and is a purely Battlestar Galactica feeling song.
Also reviewed at http://carryyouaway.blogspot.com - select tracks up for download.