To do this, they've got a great set of tools that the community can work with. What this means for level editing is that users can make quick changes to a map and won't have to wait for long compile times to see those changes - the script will load the changes on the fly.
Effects editing is also easy to do, again because it's done via scripting.
Spline nodes and other camera techniques can be very easily set. For those that used Keygrip2 for Quake 2, the manipulation of the camera is as easy or easier. Sounds are added in, once again via scripting, and loaded at runtime. Adding sounds to a level will be an easy process of simply dropping them in where you'd like or editing it via the scripting system. The Combat System FAKK2's animation tool - making your models dance a lot easier.