Harvest Moon is great, and although the concept may seem similar to those who don't really envelope themselves in this type of game, they really aren't too similar. Sure, you live in a town, interact socially with those around you, and try to "make it to the top" so to speak. In Animal Crossing, you accomplish such by collecting all there is to collect, and by participating in the special events. The same could be said for Harvest Moon, and despite the "cutesy" exterior, at its core Harvest Moon is an economics sim. Upgrading your farm and your tools yields more successful results. [Note:I am explaining this as though you have never played a Harvest Moon game before, so forgive me if I am breaking it down too far].
In Animal Crossing, you don't really have very many consequences for unaccomplished tasks. You take your time, do what you feel like, and can spend an entire day digging holes looking for treasure. However, in Harvest Moon time is your enemy. Your goal is to create a successful routine and balance your time evenly. You have crops to tend, animals to take care of, and even a family to raise. Spend the whole day watering your crops, your cow may be pissed and give you poor quality milk. Too focused on your animals? Miss too many watering cycles on your crops and they will wilt away.
Then there is the matter of the family. Not only do you have to tend the crops and take care of the animals, but you have to keep the wife happy and make sure you aren't neglecting your child. Harvest Moon is a series based on timing and taking your real life away. What I am trying to say is that it is very time consuming. Just because you like Animal Crossing doesn't mean you'll like Harvest Moon, but you'll be more open minded to it. The game has a slow start, but once you get a solid routine going, learn what crops grow in what season, learn recipes, how to cross-breed seeds, throw in some fishing, take care of all your animals, pace yourself and make sure no one gets sick, you are golden. It takes a lot of good balancing skills =)
There is a ton more that could be said about Harvest Moon, but I am trying to be brief, and if you have any other questions I'd be more than happy to answer them. It's a good game, good series, and definitely worth taking a look at...but it's not for everyone.