I did get a chance to ask a few questions about the editor and watch as Dave Ewing demonstrated what some of the changes were. Not being a mapper myself, I can only relay what was shown to me and probably not in the most technical of terms. Look for an upcoming feature from Sparky on Ued for more information.
The first thing I noticed about the new editor is the splash screen, obviously, but that's not important, so let's move on. The next thing I noticed were the dozens and dozens of prefabs being used in the new maps. Dave explained that with maps this visually complex, it was absolutely necessary to use these prefabs creatively to get all of the detail while still keeping the time to build a map reasonable. I watched as he clicked on sections of a bridge in a map he was working on. Each section was like a building block that fit together seamlessly. Any of the sections could be resized, stretched, reskinned, or otherwise manipulated to make them fit the need, and to keep them looking fresh.
With maps of this detail, there are obviously going to be dozens of places in every map that players can get stuck. Have you ever walked down a hallway in Unreal Tournament and kept "sticking" to decorated walls? In CTF-Dreary for example, there are tunnels on the middle level with "ringed" walls. You have to carefully avoid bumping up against the walls or you will find yourself suddenly stopped. To deal with this problem, they have begun using Collision Meshes. Basically, a collision mesh is wrapped around a decoration, prefab, or any object. When a player touches one, the engine knows to just allow them to move right on past the object. You still "bump" the object, and your player model actually moves around it, but it keeps the player model from just coming to a halt because it has bumped into a small pipe on a wall for instance.
The new terrain editor looks remarkably easy to use. To change the height or shape of the ground, you simply select the node and then move it up or down. The results are remarkably realistic and it takes very little time to do.
Bot pathing is still accomplished by nodes but more instructions have been added so that they can play smarter. Assault path nodes and Scripted path nodes have been added. They allow bots to do more than just run from point A to point B, attacking everything in their path. You will now see bots gather at certain points to prepare an attack, translocate and ShieldGun jump more, and generally act less like bots.