Tony, this is for you…
The Megami Tensei series (aka MegaTen aka Shin Megami Tensei aka SMT) is a long running RPG series from Atlus. There are several different offshoots from the core SMT line, which tends to be a post apocalyptic setting with lots of nasty demons running around. To my knowledge, the only game in the core line that has come to North America is SMT: Nocturne.
The Persona games are more like a dating sim crossed with a dungeon crawler. Spending time with your friends and getting to know them is almost as, if not more, important than leveling up. The last two entries (Persona 3 and 4) are some of the best JRPGs to hit the PS2, period, and are refreshing in that they’re more about the storytelling and characters than they are about phat lewt. Persona 3 was infamous for the fact that to unleash your characters’ personae (ie. cast spells) your character would have to shoot themselves in the head with a gun-like implement.
Digital Devil Saga 1 & 2 are set in a post apocalyptic cyberpunk kind of setting.
Devil Summoner games(at least the ones that have seen the light of day over here) are set in the 1920’s with you playing as a sort of private investigator. There are other ones in Japan that are set in a more cyberpunk setting.
Devil Survivor is a new DS game that looks like a mixture of the Persona games and the core series. The main plot point is that it takes place after an apocalyptic event that the authorities were able to avert. Unfortunately for you, they averted it by sealing off Tokyo with all of the demons and citizens inside it. And you’re one of the people stuck inside…
One of the biggest conceits of essentially all of the various SMT games is that while you do fight monsters and demons of all sorts, you also tend to have some way of recruiting them to your team. Some of the games have you negotiating with the demons mid-fight, others have you finding cards and fusing new demons and monsters. In essence, it’s like a very dark, mature take on Pokémon…