What are the differences between Harvest Moon and Rune Factory? I haven't really gotten into either series but I'm thinking of trying either A New Beginning or Rune Factory 4. I know Rune Factory has dungeon-crawling elements, but how well are they implemented?
I haven't played RF4, so this is just based on RF3.
The farming aspects are a bit simpler in RF than HM, but they make up for it by expanding into the action RPG genre. Outside of town, there are a few "dungeon" areas where you can gather materials, mine, fish, chop wood, and fight enemies. You can't really ignore the enemies (they'll attack you), and they drop materials when you defeat them, so fighting is part of the grind.
Combat is typical 2D hack-n-slash stuff. There's different weapon types (eg: shortsword, longsword, spear, axe) which behave differently when you swing them, and there's also magic spells. Weapons and equipment can be forged and upgraded using the materials you gather. Your character has typical RPG stats like HP, RP, strength, vitality, and intelligence, which increase as you level up your skills.
To elaborate on that, your character has various skills, some of which are combat-related (eg: shortsword, longsword, fire magic, water magic), some of which are not (eg: farming, logging, cooking, forging). Your stats increase as you level up your skills, even if that skill is not combat-related. For example, your max HP and RP will increase as you level up your logging skill.
The farming and the combat aspects integrate fairly well. As explained above, working on farming, logging, etc. will increase your stats, which will help in battle. The food you cook can also boost you in battle. But I would say the focus is more on the combat side. I would describe RF1-3 as action RPGs with HM elements, rather than HM games with action RPG elements.