Yes it is. I've got Harvest Moon for the GBA, DS, PSOne, PS2 and GameCube, so take my opinion with a pinch of salt.

I love it!
Harvest Moon is basically a farming sim with cutesy stuff thrown in - so be prepared to spend lots of time howing and sowing and watering your crops. The real fun/ reward comes when they've ripened and you can pick them.
Or you could concentrate on raising your animals - dog, chickens, sheep, cows and horse. Milk your cows and when they're big and strong and lurrrrve you, you'll get lots of milk from them. Same with your sheep and chickens. Enter them into competitions for trophies and better milk/ products.
Woo your sweetheart with gifts or turn them off with rubbish or fish bones. Get in with the villagers by giving them gifts and talking to them and they'll unlock things in the game.
Each day is also about 15 minutes long so you can play on a bus journey or something and it doesn't take long to get engrossed in your life on the farm and your animals.
So yes, definitely get it for your girlfriend.
