The favorite button is probably one of my most anticipated GUI changes in a while. No longer will I have to switch to Monster Box mode to favorite or unfavorite monsters and have to redo my sorting and filtering settings. Of course, there are a ton of other features that could severely improve QoL — like box tabs, the ability to drag select multiple monsters for selling and a better way to control what shows up in your friend slots — but for such a minor change, this is quite welcome.
Also, I don’t understand why they ever took the ability to switch between dungeon types away. It’ll be a bit more annoying to cycle through everything once ranking and multiplayer dungeons are implemented, but the option should’ve never been taken away.