I love Rune Factory, have played very little of 4 but "Rune Factory: A fantasy harvest moon" From ds caught my heart, Raguna especially and the brides.
The key difference with Harvest moon is that not only do you have to use "Runeys" to choose a balance to get crops, but also you have the chance to adventure on dungeons using magical weapons and spells to get across dungeons and get relevant items to use in alchemy and even in characters' wooing and storyline. This concept became a reality, in the late harvest moon games and early ds(I don't remember which) you had to cross a dungeon to see one of the hardest brides, the harvest goddess and then they made it a spinoff and it was a blast. Also they have antagonists which you have to beat unlike the Harvest Moon which is just making a life or saving the land in some cases.
Monsters: Elefun, Mamoo, Buffamoo, Wooly, The golem and The tiger and wolf series because one does not simply leave out monsters you can ride! I'm replaying Frontier and I have tides of Destiny for PS3.