I first played Harvest Moon on the SNES waaaayyyy back when... I fell out of touch with the series until I bought a DS in 2006, and Harvest Moon DS was one of the first games I got. I enjoy the heck out of that game still, but have avoided the other versions because of their dependence on the stylus for everything. It is a very deep game, and without some of the walkthroughs available I wouldn't know much about some of the interactions and what they unlock... I was quite surprised by the complexity of the game.
I have heard rumors through the last couple of years about Natsume toying around with the idea of making a Harvest Moon MMO, but haven't found any concrete evidence to support it. It would and could potentially be a FarmVille killer, and certainly something needs to knock Zynga on its ass for online farming. Granted, I can't see Natsume dumbing the game down to a FB app because you know they'd need to sacrifice something to make it run smoother for a lite browser-based application, but even a mini-Harvest Moon would certainly make a dent in the number that FarmVille attracts.
As long as Natsume develops a Harvest Moon on the DS in the future that doesn't rely completely on the stylus, I'd be happy to buy it.