Oh man, some great posts are showing up in this topic! 

Chris, Swamp turns the 3D landscape (well simulated 3D) and represents it from a top down view.  I was trying to think of how to describe this transition to someone born blind, and I may have a method that will work.

Imagine you are taken to a tank shaped as a large box.  Someone has cut a hole in the side of the box, allowing you to reach your hand inside.  Your hand hits 2 metal bars that are sitting vertically in the tank.  There is not enough space to fit your hand around the bars, but you are able to put your fingers between them to feel past them a short distance.  When doing this your finger tips graze 2 more bars that seem to be in the same position behind the ones you can clearly feel.  If you had to describe the insides of the tank, you would say there are 4 metal bars in a 2 by 2 pattern.

This would be called first person perspective in a video game.  You are down at the level of the characters and objects/enemies in the distance can be completely hidden or partially obstructed by closer objects.  Light cannot get past the closer objects similarly to how your hand cannot reach back to feel what is behind them, so a sighted friend standing next to you would actually share much of the same information you had about the box's insides.  From his visual perspective, he would also see the 2 closest vertical bars, probably the edges of the bars behind those, and depending on their sizes and positions, anything behind those could be completely hidden for him too.  A difference with sight is that it isn't limited by the length, or thickness, of one's hand and fingers.  Your sighted counterpart would almost certainly be able to view further into the box than your hand was able to reach.  Where your hand stopped and was only able to graze the second set of bars, his vision would allow him to continue "reaching" until there was literally something blocking the path completely... or the box was too poorly lit as he looked further toward the back.

Now you remove your hand and are asked to reach down through a different hole in the top of the tank.  You reach down with your flat hand and it comes to rest on the tops of 6 cylinders.  To you, the 6 "dots" are basically laid out like a braille cell.  The bars are too close together for your hand to reach the floor between them, so from this position there is no way to tell how tall the bars are.  The best you can do is rest your hand along the top to feel how many there are, and how they are arranged.  In a video game this would be considered top down perspective.  A sighted friend looking down from above (where you are reaching down from) would experience a very similar scene to what you have felt.  He would see the 6 bars laid out in their pattern, and would likely only be able to estimate how tall they actually are.  I'm simplifying things for these examples of course, but in general the sighted and blind people would share most of the same limitations depending on where they were standing.

Each has its own set of advantages and disadvantages.  Between these 2 perspectives, first person perspective granted the largest advantage to the sighted person.  Your ability to reach inside was more limited than his ability to see inside, since he would potentially have been able to see several sets of bars had they continued going deeper and deeper into the box.  In Swamp, this would have been the equivalent of standing at the gas station and being able to clearly see zombies on the far side of the map at the factory.  The advantages over the blind players would have been too great for fair play.

Now as far as top down perspective goes, I'll elaborate by talking about a chess board.  Once again for the sake of examples, you carefully lower your hand from above to feel for the position of pieces on a chess board.  Perhaps it is a game some people were playing and have walked away to take a break.  Assuming the 2 teams have pieces made of different materials (that can be felt), you would be able to carefully recreate the board and the positions of the pieces in your head.  Trying to do the same from a first person perspective would be a nightmare, and in all likelihood would never really be possible.  The closer pieces would block those further away and you'd never really get a clear image of where everything was.  Your sighted friend would have literally the same problem, and would always choose to play Chess from a top down perspective.

When you looked at the board, we can assume that you worked your way across it, lowering your hand to feel each part of the board before moving on.  This would take some time, but it can be worked out.  Your sighted friend will work almost like having an extremely large hand, that is highly sensitive.  He will be able to view the entire board at the same time, similar to how you could place your fingertips on a few braille characters and read them instantly.  For the human hand the finger tips are the best part at picking up tiny details, while your sighted friend's giant magic hand of vision is most sensitive at its very center.  The further out toward the edges you go, the less reliable it is for fine detail.  At its outermost edges it is quite numb, and can miss all but the most obvious of shapes.  It is referred to as peripheral vision, and generally only helps people avoid walls and bumping into people... though sometimes that even fails, haha!  Our eyes move around because we are constantly trying to put that most sensitive "center" onto what we care the most about, which is equivalent to how you likely move around your hand to keep your sensitive finger tips moving to what you care about the most.

So clearly the ability to view the entire chess board at once gives your sighted friend an advantage.  In essence, his hand is just far larger than yours, so he doesn't need break down the whole board into parts and check each one.  For Swamp, the solution I went with was to simply shrink the size of his hand!

Normally lets say you can feel 12 (3 wide and 4 long) squares on the chess board with the size of your hand.  I know I'm not describing how you'd actually check the board but lets pretend for a moment.  It would take you 6 times of lowering your hand before you had felt the entire thing.  Lets say that normally your sighted friend could "feel" 256 squares at a time (16 wide and 16 long), which is far more than the chess board even has.  To make things more even, I shrink the size of his hand (field of vision) so that he can only feel 4 squares (2 by 2) at a time.  He can process what he "feels" faster than you can, but you can now actually feel an area 3 times in size each time.  The goal was to get you and he to take approximately the same amount of overall time to figure out the whole board.

I've gotten myself a bit far from the original Swamp path, so now I'll back track to hopefully pull this all together and make sense.  Swamp is presented as a first person perspective game in audio.  The player hears the world as though they are down inside of it.  To the sighted player it is visually displayed as a top down perspective game, where they view it in the same way they would look down at a chess board.  In an instant a sighted player will be able to see the positions of all the pieces, which would be loot, walls, zombies, and other players.  This would normally be very unfair so to counter this I have lowered the field of view, causing their "hand" to shrink.  At any given time a sighted player can only see a 20 by 20 grid of tiles, with their own character always at the center.  To move their hand they must walk their character, to know what is further in that direction.  This means they will always instantly know everything that is going on within that small space, but they cannot use their vision to shoot at zombies or hear loot outside of it.

To compare a blind and sighted player more directly, a blind player will regularly shoot zombies that are 40 to 60 tiles away in distance.  The sighted player will have no idea the zombies were even there, and their blind team mate will have already aimed at and shot them!  When up close, the blind player may need to take a moment to figure out exactly where the loot is, or may have to use radars to know how the hallway curves to the left.  The sighted player will instantly know exactly where the loot is, and exactly how the walls of the building are positioned.  Depending on the situation, either the blind or the sighted player will have a massive advantage.  I never found a way to truly make the players equal, but I did find a way to put them into different roles.  With each type being good in a very specific situation, back when I was designing Swamp I hoped one day many sighted players would be in the game as well, regularly pairing up with blind players to form teams to excel in all situations.

You play an RPG and your party will likely have a healthy mix of armored melee guys and ranged support, so you can handle whatever comes at you.  I hoped that one day Swamp would be teams of blind and sighted players for that very same reason.