The differences include textures raising to 1080p (you know, how even in the latest custom delivery area, the textures in Labyrinthos have some pixelated areas). That itself is not anything special but it will remove a lot of the random low quality stuff that we see.

The material will look more realistic, more lights can be added to display more of what is already there, more objects can be added for detail (such as boxes, pipes and other detail), shadow rendering will be longer and shaders are being improved which is what will make one of the greatest impacts, because shaders are what make use of your GPU's modern capabilities.

It is pretty accurate to say that characters aren't changing much other than a slight shader improvement and 1080p textures and that's because they can't anticipate how many players will be in one area at the same time, so they have to change them with the assumption that a massive crowd of players is present with these changes (they showed in one of the developer panels a huge army of characters in their test environment). With everything else, such as the areas, they can set hard limits on how much they do certain things so that it doesn't exceed their Recommended specs. Other than that, they don't want to spoil the image you have of your character, so if they made it look realistic, you might be attached to how it currently looks.

So you're going to have to focus on improvements to things that aren't the player character in any future graphic updates tbh.