NOT in the same vein as Harvest Moon, but a solid addicting time-waster, nonetheless. Recommended.
How does RIver King do at that? OK. The game isn't bad. the graphics should be better at this stage in the DS's life, but Natsume prefers to focus on the cutesy, family friendly theme, which generally requires less complex graphics.
In River King, you have an extremely dumbed down fishing sim built into a mediocre RPG backdrop. This isn't a fair description of the game, however. The game is extremely addicting and fun. The monster companions add a needed element to the game, all the characters are lovable and their roles relationships develop throughout the story, and so on... That's another thing by the way. This game has a story, whereas Harvest Moon games generally do not focus much on story or plot, you are constantly triggering story advancing cut-scenes.
The story itself was probably based on some old Japanese legend because it sounds so familiar (or cliche). The RIver King is an ancient fish that swims the valley where you live, and you have to find it in order to heal your sister who has mysteriously fallen into a mystic coma. Along the way you meet friends, allies, and rivals, some of which are also pursuing the elusive fishie.
Now that that's aside, let's talk gameplay: The gameplay is addicting. It's not good, nor does it ever claim to be. It just succeeds in being very addicting bcause of its simplicity. Every time you are in the fish-catching minigame, for lack of a better word, it plays out basically the same, with an occasional, but never unbearable, notch in the difficulty. Basically to catch a fish you draw circles on the touch screen, and when you see the fishing line's tightness gauge getting too high (meaning it may break), you stop for a second and wait for it to go down a bit, but not al the way to the bottom because then the fish will snap the line if you're not careful.
That's the game in a nutshell. You catch fish, collect bugs and flowers, train monsters and level them up by feeding them fish (the first one's final form is a Fox Babe, if you're into that kind of thing). You buy new rods, lures, bait, flies, collecting fish cards, earn points (the currency), etc. There's not as much depth to this game as Harvest Moon, but there is enough to keep you busy for a while. If you go into it with a clear head and no expectations, you probably won't be disappointed by the lack of variety and inability to do such things as upgrade your house of get married.
My criticisms of the game generally address what the game COULD'VE been. It could've had special fish caught via a different minigame, a netting minigame for fish in the shallows, going out in a boat on the lakes to get fish in the deep you couldn't otherwise reach, a bug catching minigame or even a net like in Animal Crossing would be infinitely more interesting than the system of "check this rock". There could've been fishing battles, where two rivals try to catch as many fish as they can in a certain period of time, or other kinds of fishing minigames.
Overall the game is just fine. I totally recommend it to someone needing to waste a little time and a little money. Then again, the new Harvest Moon for the DS is coming out in August, and I'm betting that'll be a bit better. Nonetheless, feel free to check this one out.
*****One thing I think is interesting is the trend (although this is not a new series) that family-based companies like Natsume and Nintendo have started toward family-friendly RPG's with limited violence to living things (unless you count fish). Another example of this is the Custom Robo series, which blends top-down RPG's with the 3d Mech battles. Then there's Harvest Moon, a farming Adventure/RPG, and Animal Crossing. Making good games like these is the future of family gaming, and I have to give this one a high score just because it's pushing that agenda.