When I first got Harvest Moon I thought it was going to be a really broing game, completly based around farming and way too easy, but I am very pleased to say I was absolutely wrong.
1) It is definetly not boring, with hundreds of things you can do and even more you have to do it is impossible to say "there is nothing to do"
2) Similarly, Harvest Moon is definetly not completely based on farming. Yes, it's a farming game, but there is so much more to do. You can collect produce, mine, get a wife, help the sprites and so much more.
3)Harvest Moon is also quite challenging. in the first month or 2 when you are struggling for cash, it does get pretty hard, but once you get into the swing of things it does get slightly easier and you can focus on progressing in the game
Basically I think Harvest Moon is the best game there is for DS and anyone at all would enjoy it. You may think it's for babies, but just give it a go and I guarantee you will like it.