Personally I found that the most effective soundtrack was that of the Quake series, perhaps the artists being some of my favourite artists helped with that but Nine Inch Nails and Front Line Assembly did a great job in creating an atmosphere of getting things done! The speed and intensity of the game was perfectly accented by the speed and intensity of the music. What I personally enjoyed the most was where Sonic Mayhem and Front Line Assembly worked together to make a variation of musical styles which cover the the different play styles of different maps. Here is a compilation of the tracks.
After the sound tracks comes the foley and voice acting which is something that is still being vitally tweaked by modern games. This video documenting the making of "The Last of Us" is really good at showing how sound is being implemented and how acting, not just voice acting, has become a vital aspect to games. The section on sound starts at 47 minutes through.