On the single player side, players a who have finished the campaign already can now start over in "master" difficulty. This new setting makes the enemies and animals much stronger and smarter, rather then doubling their numbers.
Those that are still playing the campaign, and those who start over, will now be able to reset outposts that you've captured, and then take them back over again. This could be done for easy XP, or just for fun. Also, some of the HUD options can be toggled on and off, making the game even harder.
On the multiplayer side, idle players can no longer be kicked out of private or custom matches and the time for map voting between matches has been increased.
While the multiplayer side didn't get as big of an update as the single player, at least Ubisoft is giving both sides some new stuff to play with.