One of the biggest changes is the reduction of maximum positive alignment from 100 to 10. This means a player will only be able to kill someone from their own faction once before they feel the sting of the "rogue player / murderer" social system, instead of letting players gain reputation up to 100 and then go on a virtual killing spree without any punishment.
The other huge change (and one of the most wanted changes) was the removal of players gaining skills by attacking invulnerable players. Before, a player could wail on another invulnerable player and quickly level their weapon skill, making their attacks more potent. This oversight has finally been fixed, but not without repercussions.
Keen of Keen and Graev has said that the invulnerable player skill up was a well known problem and has lead to significant abuse. This means players who may not have taken advantage of that bug or new players to the game will not be on the same level as other players on the server. Aventurine has also removed the ability to gain weapon skill from the starting weapons, making it even harder on new players to gain skill. It's unclear as to how Aventurine will deal with this large imbalance of power, if they will deal with it at all.
The patch also introduces some other fun changes, like the inclusion of gates on cities and the ability to unbind people from clanstones you own. Check out the full patch notes on the Darkfall forums, and also check out Keen's overview of the changes on his blog.