For anyone who cares.
The plot and characterization are supposed to be much deeper than previous games. The plot is also broken up into 3 parts. The first two are the "main story" and the final part is more of a "bonus story." The final part is activated at random. Several marriage candidates can't be married until you've finished certain plot points. Some characters are actually boss monsters who are turned into humans after you defeat them.
You can date people once you raise their affection to around 7. They may ask you out instead. Once you reach 10 you can give them an engagement ring and propose. Proposals are lengthened in this game. Some characters may propose to you instead. Have fun turning down the ones you were shooting for "just friends" with.
The ability to take villagers with you into dungeons from RF3 is still a feature here. Several areas actually can't be cleared on your own. Once you have a child they'll also be able to go into dungeons with you. You can get married and have your kid before finishing the storyline.
In addition to earning money you also get "prince points" for performing your duties as the prince/princess. You get 1 point a day whenever you talk to people, up to 100 for beating monsters and... I don't remember the other things you can do. Sorry. Prince points can be spent to have new stores added to the town, or to add festivals. You can also use them to purchase a larger rucksack.
Chlorica: A butler (maid?) in training. She's supposedly quite talented and hard working, but has trouble staying awake.
Dolce: One of the bosses turned human. Her monster form is called Marinetta, and looks like a... well... like a marionette. I don't know that much about her personality. She sounds like she's similar to a tsundere type, but not quite.
Forte: In charge of guarding the town. Since it's her duty, she'll accompany you in dungeons even if you aren't close to her. She's apparently stubborn but seems to have some insecurities about not being feminine.
Kohaku: Another boss turned human. Her monster form is called Ambrosia, and looks like a butterfly. She's the first boss you fight. I'm a little unsure of her personality. Most info described her as childish, but some people were saying she seems wise on a whole different level.
Margarete: An elf bard working at the restaurant. I don't know much about her, but I believe she has some relation to the de Saint-Coquille family. Either an adopted daughter or like a daughter to an actual member of the family.
Xao Pai: The daughter of the bath house owner. and token easterner for the game. I don't know much about her personality. She seems to be the cheerful one for the girls.
Arthur: A nobleman. It seems that he was supposed to be the one to run the town, but after some confusion where the job is given to the main character he's happy to let them handle it. If that sentence didn't make it obvious, he's a laid back person.
Doug: First dwarven marriage option in the series. The games clearly don't like the "racist stereotype" Micah mentions in RF3. Doug has nothing obvious to do with forging, and runs the general store. He's apparently somewhat mean until you finish the first two parts of the "main story." Until you do you can't raise his affection past 3 points.
Dylas: Another boss turned human. He's the second boss of the game. His monster form is a black unicorn named Raiden. He likes to fish, and will work as a waiter in the local restaurant. He's apparently not too talkative, and awkward with his words. My understanding is that he's the character who's most likely to use innuendos as well.
Kiel: The shota character. He's Forte's studious younger brother. I don't know much about his personality but I suspect he has some relation to Leon's character.
Leon: The last boss turned human. He's the final boss of the first part of the plot (meaning you must get that far into the game just to meet him.) His monster form is a sarcophagus, but he has fox ears and a tail in human form. Somehow. He looks like a very serious character, but apparently enjoys teasing people.
Vishnal: A butler in training. He's very passionate about his work, but apparently the worst chef in the game. If you marry him he'll give you either a fail or a super fail for breakfast each morning. If anyone is familiar with Ouran Host Club, he's described as a less flamboyant version of Tamaki.
Bade: The town blacksmith, who doesn't care much about his job.
Blossom: The general store owner who's in poor health. She seems to think fondly of Doug.
Illuminator: An elf. I think she owns a flower shop, but I don't have much info on her.
Jones: The town doctor. He has a fear of blood.
Lin Fa: Xao Pai's mother and owner of the bath house.
Nancy: Jones' wife. She helps with his work.
Pico: I... don't really know. I think she's some sort of living doll who hangs out with Dolce.
Pocoline: His name might be intended as Porkrind. He's a chef from the de Saint-Coquille family, and looks about how most of the family does. He was apparently very attractive in his youth.
Volkanon: The head butler. I don't know much about him.
Ventuswill: The air dragon. She accidentally assumes you're the member of the royal family who was supposed to come run the town.
Well, I don't have the game myself, and I've been trying hard not to read any plot spoilers (though I have accidentally picked up a few bits and pieces) but that's what I've managed to gather from the wiki and from various forums. All I can really say about the plot is that the ending is supposed to be either incredibly sad or bitter sweet, depending on how you interpret it.
edit: Something else I just noticed. An older version of Ethelberd (that guy from the Sech army in the vary first game) is a character in this game as well.