I may have mentioned this before, but it's worth restating. I was looking at my computer's background, a painting by Caspar David Friedrich called Moonrise by the Sea, and considering the illusion of perspective artists create by making objects in the background smaller than objects in the foreground.
It reminds me of an element that seldom appears in games and is sorely missed: a thorough perspective of sound.
When I was young, I watched nature shows all the time. I was fascinated to learn that a lion's roar, an elephant's trumpet, or the howl of a howler monkey can be heard from over a mile away. When walking in the woods, I can hear not only what directly surrounds me, but creatures and events a great distance away.
Current games commonly make use of positional audio and surround sound. But they still tend to offer the player only those sounds immediately around the character. In Gears of War, the player catches fleeting glimpses of great monsters and bosses levels before having to engage those enemies. The same thing can be accomplished with sound...and with the added value of inspiring the player's imagination to create its own figures of horror.
Extended perspective of sound needn't be limited to frightening sounds, of course. A howler monkey, for example, is hardly a frightening animal. The effects of creature noises can range from the frightening and disorienting to the angelic and inspirational. There are also environmental sounds such as waterfalls, landslides, encroaching thunder, the easy to misinterpret wailing of wind, etc.
Distant sounds can even be used to have more direct non-mood effects on player actions. Suppose the player is unknowingly surrounded by many creatures of a particular type, but only one voices a call at a time. The player may hear noises to the north. When he crosses a particular threshold, the noises shift to the west (different beings, but of the same voice). This could be used to disorient the player, leading the player to believe he is tracking a particular individual when he is actually being led in circles...or toward a trap.
One of Oblivion and Vanguard's big selling points is the vast range of visibility it offers to its players. It would be nice if game developers would employ the same range of player perspective with sound effects as they do with visuals.