First major update is for the Infernal Machine. The machine is first assembled by finding the necessary components; after which it unlocks events and challenges which now features two bosses.
The difficulty level for this has been increased and the bosses have undergone visual changes. Defeating these bosses will drop gold, magic items and the rare components for a legendary ring.
An update to Monster Power will “increase the health and damage of monsters according to different ‘power levels’” resulting in better experience, gold and magic find for every power hike.
The Demon Hunter class has received much love in the new patch. Many basic skills like Bola Shot have been buffed; as well as their pets who now have increased damage.
Changes to Nephalem Valour stacks makes it so that contents of Resplendent chests and dropped loot in Inferno events will respond to the number of stacks you’re rolling with at the time.
You can read the entire changelog by going to the official forums.