Possibly the best Harvest Moon in the series. If only the newer games were of this level.
Now, Harvest Moon definitely won't appease everyone's appetites, but those looking for a relaxing farming simulation (haha) have found their match. You start off playing as your father's son, who has inherited his farm. You will start off getting a tutorial, and then will proceed to live on the farm for a long time. Each day, you will have to tend to your animals, gather resources (whether it be for cooking, cash, friendship, or even romance!).
Quite early in the game, you will have to pick one of three bachelorettes to marry, or it's game over. This game soon evolves so your new spouse will move in with you, and you can and WILL also get a child. The game evolves by changing chapters (which span a couple of years). In each new chapter, new characters will move in, and out of the village, everyone around you, and especially you, will age and show change. It makes for a memorable experience. Anyway, moving on..
For the GCN, this game's graphics are top-notch, and I still consider them to be really good. Nothing Final Fantasy-esque though, heh.
The soundtrack in this game. Oh my god, you'll definitely fall in love when it comes to the music. It might make you sad, relaxed, upbeat... but one word that can definitely describe it is "good". Also, the majority of the sound effects are good, such as when you hear cows moo.
Replayability? Try playing through the whole game first, then ask that again.
Anyway, this game is one of the most amazing in the series, partially because this is a unique experience compared to ALL of the other HM games (except Another Wonderful Life, which is basically the same as this, except you play as a girl and there are a couple new features), and it's just a really relaxing game.
So: if you have a Wii or a GCN, and haven't played this (also assuming it sounds even somewhat interesting)... Try getting it, you won't be disappointed.