I agree with most of what Dale said, but I think he doesn't give enough credit to JC where it really shines, which is the incredible craftsmanship that was devoted to it. The graphics and animation are well executed, between the rendered 3D polygon images (real-time and pre-rendered) and the hand-rendered anime distinct character designs that feel more Miyazaki-esque (rather than the typically over sexed goo-goo dolls that normally populate Japanese games). The sound and music also retain the primitive backwaters village style set forth in graphics, making for a much more cohesive presentation unlike the visually muddled Star Ocean: The Second Story. JC, in terms of its visual and aural aesthetics, is clearly on par with any recent RPG entry.
The background plot is very complex and richly detailed, yet logically silly the way folklore typically is. I could tell that much careful attention was given to the setting and story. This, in turn, not only made me gravitate more toward the game, but my devotion to the story didn't seem cheaply spent either. It's also brilliant the way historical myths were unfolded to me via the elders of the village in a verbal storytelling session. The story elements are only furthered enhanced by some of the finest voice acting in a game that quickly garnered my attention.
In terms of actual gameplay, JC isn't quite the sprawling trek that most RPGs represent. Instead, traveling is minimized through menus and plot devices that enable quick entry to particular areas. There is some exploration, but the main focus still resides on combating and capturing monsters (as Dale already mentioned, unoriginally dubbed Minions). Combining various monsters in order to reach higher peaks of combat prowess is a fun and often addictive experience. And while the Minions don't have nearly as much personality as Pokémon do, I still found myself engaged in the process of training and evolving my Minions. This is definitely not a shameless rip-off of the Pokémon concept and it takes only a few combinations of Minions to realize that serious detail in the process was not sacrificed.
It's too bad that the JC's focus largely remains on a single village which makes for a well streamlined and efficient design, but comes up feeling positively underwhelming. Add to that the fact that Crave Entertainment didn't devote much marketing resource (the game barely registered on my radar when it was released), the game was released rather uneventfully and, hence, destined to be a sleeper hit. It's too bad that such a well-crafted game gets largely done in by not being hyped and thrust into the forefront of public conscious the way I feel it richly deserves.