My gut feeling is that Secret of Mana is an RPG whereas Castlevania II is not. But I have a hard time coming up with any objective criteria that would exclude C2 but not SoM. Both games:
- Have level advancement
- Are not linear, but require exploration
- Have "safe" areas like towns
- Have equippable weapons and shops
SoM has more of a story than C2 but not all RPGs have great stories.
I notice that neither Zenic Reverie nor Shen Nung included C2 in their list so I'm not alone in this, but I'm struggling with why.
This is mostly relevant because there are some games that some sites label as RPGs that I think are very marginal or possibly not RPGs at all. I guess when I get to them I should just play them for a little while and see what I think.