Dark Cloud 2 did it for me. I hate the fact that most RPGs are linear and force to fight the same lousy enemies over and over, but DC2's Invention System has changed me into an RPG fan. The Invention System lets you photograph household items and combine them, like making recipes in Harvest Moon 64 and Save the Homeland. Also, it's got weirdo characters. I probably won't play it again once I beat it.
I always liked both of those Harvest Moons, but that series reminds me more of a game like Shenmue with a lot of experimentation.