WoW Classic will use the modern Legion/Battle for Azeroth client with its more advanced graphical options, and the ‘Classic’ button allows players to switch back to the original Vanilla graphics from 2004. Compare the graphics by sliding on the images below.
As seen on the slider images, the modern’s client Ultra High settings result in more detailed environments, denser foliage, and enhanced shadows.
Classic vs. BFA Graphics
Classic vs. Vanilla Login Screen
Here is also a comparison between the original World of Warcraft “vanilla” login screen used between 2004 – 2007, compared with the new World of Warcraft: Classic login screen. Notice any difference?