There are many new features like Lumen and Nanite, but also greatly improved environment, a redesigned Unreal Editor, better performance, artist-friendly animation tools, an extended mesh creation and editing toolset, improved path tracing, and much more. See the documentation for full details.
I was working on procedurally generated Universe. It’s obvious that you cannot show everything at once to the player (like chunks in Minecraft). There is observable Universe in AstroColony which shows new planetoids, it’s size, resources and biome type. All at your fingertips.