Elwynn Forest gets a fresh look with Forever's graphics update: rivers that now flow.
What we know
Blizzard used Elwynn's rivers as the example of the new water: they now flow, bend around rocks and foam when they hit things (press).
Blizzard is not changing the art style (“we believe WoW Classic's art style is timeless”); the work focuses on environmental effects.
The official fact sheet lists global illumination, volumetric fog, god rays, water that flows and catches the light, and terrain that casts shadows as the sun moves.
At the “Evolving a Timeless World” panel they said draw distance is longer: from the Wetlands you can now see Dun Morogh (press).
Blizzard admits the trailer leaned on sunrise and sunset: “not every zone is going to be set at sunrise or sunset all the time” (press).
What changes
Rivers that now flow.
Part of the rendering update Blizzard showed at BlizzCon; the game includes an HD/SD graphics toggle.