Sound is an overlooked and essential part of games. It is such a natural thing to hear sounds we recognise in games such as trees rustling, footsteps crunching on gravel and the splash of water. But because the sounds are so real they become an invisible form in games and if they weren't something would feel wrong. I mean my own personal experience playing the recent Call of Duty on a friends PC was very different as his sound wasn't working and I put the game down as the atmosphere of explosions and bullets firing past my character wasn't there and I felt detatched from the action.
I really enjoy the soundtracks for games in general as they are very different and I find they are enjoyable to work to as a lot of the time the songs are purely background music without lyrics and usually classically composed and have a lot of story through them. Games are usually easily recognised by the songs that accompany them, If someone puts Halo on in another room i will know as usually the loud and dramatic orchestra will be blasting trying to break the sound system its coming through. Though even if i can't hear the title music the iconic sounds of the plasma grenades or the blast of the generic assault rifle is enough to be sure that someone is palying Halo without me.
Another game that sounds are easily recognisable is Metal Gear Solid, I mean the warning sound of the guards with the most ridiculous "!" symbol over their heads when they spot you is classic and anyone who has played it or seen a friend play will instantly know where the sound is from. Hideo Kojima has an entire orchestra that works on his games and they even hold concerts with the game playing in the background for fans of the game and the music alike!
Sounds in games have always been limited to actions that happen in game based on whether the character does something to effect the environment. I mean most gamers will remember the Mario coin blip and the Sonic spin as he went into a ball but what about the more realistic games. Sounds always seem the same and never appear to change as they do in real life due to the nature of being pre recorded.
Its a shame that the technology for sound in games hasn't been improved, I will say the quality and crispness does get better as time goes on. The sound systems for TV's and surround sound systems improve but as with many other aspects of games today it could be pushed easily to another level.