New Features:
The love element is said to be improved, including embarrassing situations for Lest and Frey.
A new romance feature named Dokidoki Zoom allows you to zoom in on the scene between you and the person you are with, with high-polygon 3D models.
There is no longer grid-based farming, so you can organize your farm however you like.
Rather than having a friendship and jumping right to marriage, you can maintain a lovers state with someone and still marry someone else.
You can have more than one lover.
There will be an Rune Factory Frontier-style anime cutscene for each bachelor(ette)'s introduction.
You can build buildings in order to attract more people and tourists to the town. The protagonist earns a rating depending on how many people show up, the starting title being 'Beginner Prince'.
The females and males will now wear pajamas.
The Prince System is used to build up your town and attract tourists as you do. Prince Points are used to build up the town, as well as holding festivals.
If you mange to build up a nice town, you earn the title 'Crown of Crown', which symbolizes you being the ultimate prince.
http://runefactory.wikia.com/wiki/Rune_Factory_4