Gamereactor asked a few questions to Evan Wells of Naught Dog about the Uncharted series and the upcoming sequel to Uncharted: Drake's Fortune.
This is what he said about what the main difference between are:
"One of the main differences is the addition our action-stealth mechanic, which is all about adding complexity, expanding player choice in our combat situations, and fleshing out our enemy AI system. "Action" represents the idea that we're trying to keep the pace up and "stealth" represents the tactics we're familiar with regarding taking out enemies unnoticed. We don't want to introduce the frustration of being forced to move at the game's (presumably slower) pace by replaying and replaying a set-up due to failing a stealth-heavy situation."
To read the full interview, follow the link below.