I never actually got the chance to play Persona 3. My attention span at the time it came out was dangerously short. I did get to experience a fair amount of it, though; my roommate at the time played the hell out of it. I enjoyed it vicariously, watching for long stretches of play and squeezing gameplay stories of of him.
You see, I love roguelikes. I have a longstanding fascination with tarot imagery. Throw in my guilty appreciation for dating sim style gameplay and you can understand why I jumped at the chance to play Persona 4. Sure, the characters no longer shoot themselves in the head to cast magic spells but aside from that disappointing change, Persona 4 is a successful iteration on a formula designed to appeal specifically to me.
For those who have not played either game, each modern Persona game is essentially two different games that play off of each other. The first is a straight up roguelike dungeon crawl. You spend your time going deeper and deeper (or higher and higher) into a dungeon. Most floors are randomly generated each time you enter them so you can't just memorize the map. Each floor carries more deadly enemies, and more valuable treasures, than the last. Occasionally there is an extremely powerful boss monster.
The second game is a dating sim/visual novel. Each day is divided into discrete parcels of time that the character can spend enhancing statistics like "courage" and "understanding", earning money, or socializing with other characters some of whom are friends some of whom are potential love interests.
The two halves are tied together first by the main plot. Both games have periodic time limits where, if some threat is not dealt with in the dungeon, there are consequences for one character or another in the "real" world. These are essentially the chapters of the game.
The halves are also tied together by the central "persona" mechanic. The system is, in fact, fairly complex. It boils down to this: player can take on the personality aspects of people he's formed relationships with, and can use those aspects in combat. For example, if he makes friends with the athelete, he can choose to be strong and resilient. The more he understands the athelete, the more resilient he can be.
This core idea is a little obscured behind some arcane tarot references and a "gotta catch 'em all" list of gods and monsters. If you're really into mystical symbolism, and I happen to be, you might get it kick out of it. I could also see where you could find the amount of detail needlessly tedious. Then again, needlessly detailed tedium is a hallmark of JRPGs.
But I digress. My point is that the dating sim half of the game provides a compelling way to link the characters and caring about the characters and the story to the gameplay itself. In general, dating sim technology is a powerful engine that can be hooked to a variety of different game types.
For an example of this take a look at one of my guilty pleasure games - Dead of Alive Extreme Beach Volleyball. Here's what you need to know: yes, it is blatant exploitation of women and their bodies. However, the core game is also fundamentally fun. In a nutshell you have to get a partner to join your team and you have to keep the partner happy so that her AI will play well. The hardest partners to please are also the best players. And to sweeten the pot, you can play as any of the players so any swimsuits you give away you can then use when you play as the other character.
Dating sim style play hooks into motivations that I don't think are fully tapped yet for gaming, unlike experience systems, high scores, other more common motivation mechanics.