Jon talks undead, specifically ghosts and the ghost-like specter and wraith. He first asks about the visual differences between the three. No mechanics, just that if you described them to a player if they could tell them apart. Based on his descriptions and art, I could say that save for the ghost and spectre yeah, they are pretty easy to tell apart. The problem is that I do not like any of the art (and disagree on the flavor material concerning the wraith).
The ghost has an exaggerated pose, like she got shoved, and I guess the sample specter's manner of violent death was by being skinned? The wraith just looks silly, with its contorted arms and massive right hand. Like the lizardfolk and troglodyte none of this art looks like that anyone was trying very hard, and I hope it all gets scrapped. Also if wraiths are spirits that have been bound to a location, why must they be depicted in armor? They could just as easily retain their appearance from previous editions, skulking about the place they must guard and ambush intruders.
In 2nd Edition the images of the ghost and spectre looked like the same old lady, just in different colored clothing. 3rd Edition the descriptions were basically the same, except the ghost entry mentioned that "in some cases the spiritual form is somewhat altered" (though provides no examples or limitations), while spectres often displayed the evidence of a violent death. 4th Edition deviated from this model by having ghosts look humanoid (or whatever creature it is a ghost of), with specters looking more like amorphous, vaguely humanoid masses of spirit-stuff.
The wraith is really the odd man out, here. The 2nd Edition picture shows a shadowy shape with roiling smoke for feet, whose skeletal face glows with an internal light. The 3rd Edition wraith looks more like tattered, black cloth with a vaguely humanoid shape. 4th Edition kind of mixed the two, giving us something that looks like a humanoid figure shrouded in black clothing, with glowing eyes and mouth.
So how would I describe them?
I am not entirely opposed to ghosts having the largely traditional "ghost" form that we have come to expect: semi-transparent, blue, white, green, etc color, and perhaps the feet are wispy trails. They could also radiate a soft glow, and I imagine that when they move their form dissipates briefly, solidifying once they stop. In most cases they would appear as they did at their time of death, so if they were injured, mutilated, or executed it would be readily apparent.
Spectres/specters are a bit more difficult to differentiate. If they were victims of violent deaths, I would want to emphasize this more. I like the direction that 4th Edition took, making them appear less composed and more chaotic. If they are so wrapped in rage and hatred, it would make sense to have their spirit forms reflect this. Maybe their eyes glow, too?
While I like the appearance of wraiths (from previous editions, that is), the idea of them being spirits bound to complete or guard something does not really convey that idea. Why not represent this angle with bracers, shackles (that either trail off or drag on the ground), runes circling their heads, or searing writing on their skin indicative of their contract?