1. New weapon ranks: Additional “Hero” weapons that are stronger than “Brave” weapons (Hero Sword, Lance, Axe, Bow, Tome and Stone). After the update, you’ll receive one of each weapon for free.
2. Leveling: Level cap has been raised to 110.
3. New weapon attributes: Strength Drain, which boosts damage after every 100 kills. It will be added to random drops after the update.
4. Blessings New blessings for the shrine: Defence Blessing, Resistance Blessing, Drain Blessing, Seal Blessing.
5. Other: Ability to buy the Fire Emblem Fates paid DLC, can now give orders to restore a fortress captain’s HP, History Mode S rank requirements have been made easier in the New 3DS version, other bug fixes etc.
In summary, there is the level cap increase, blessing additions and just general improvements to the overall game. If you want to read up & keep up with the patch notes, visit their update notes site here.
Friendly reminder to grab some lance & bow materials for the 3 new characters, the last history mode map with the previous free update is really good in that regard and will continue to be onward from now.