The update comes as the first DLC package (called Operation Broken Eagle) will be released later today. Operation Broken Eagle is the first in what is being described as episodic content that will extend Dead Rising 3. From what we hear, there is no co-op support offered in this DLC package.
According to what we have been able to uncover about the update, specifics include fixes related to the Achievements, as well tweaks aimed at fixing the UI and SmartGlass problems. One major enhancement is the addition of the new impulse trigger feature that will let players know when they are low on ammo by the trigger vibrations.
According to the developers at Capcom Vancouver, additional work has been done to address issues where the frame rate had fallen to below 30 fps when there were too many objects on the screen. This work has led to a much smoother gameplay experience and better graphics performance from our understanding.