"If they lose eye contact with Drake for a few seconds, one or more enemies will start hunting around the area, starting with his last known location, and then spread their search out if he's not found." This hunting behaviour means that the enemies will need to be able to follow Drake wherever he goes, which means jumping and climbing around the environment. "The benefit to this was our combat wasn't limited to flat terrain anymore."
Sounds great to us. One of our biggest gripes with Uncharted 1 was that at any given point you were either fighting or platforming. Hopefully we'll see more of a crossover in the sequel. Apparently more details will be forthcoming once CVG posts the full interview with Straley tomorrow.