Breath of Fire.
I think the tragedy of Breath of Fire for me is that the game that "killed" the series, Dragon Quarter, is actually a fantastic game. I think Dragon Quarter has even been vindicated a bit over time--people hated it when it came out, but these days I mostly see people gushing about it. Breath of Fire 6 apparently exists as a browser game, so it's more of an undead series than a dead series, but man. Breath of Fire was amazing while it lasted.