Audio is an often overlooked part of game dev. Other than sound effects and music, <i>how</i> that audio plays is important. Spatial audio is a <i>must</i> for FPS games. Less so for The Sims. Most engine devs (myself included) just stuck with 2-chan spatial (as in, the pan L/R is the angle to you from your facing direction) with just simpleton software estimation of 3d space. No doppler effect, no reverb, just barely EQ. Kudos to Valve for giving us something other than XAudio and FMOD!