#but seriously - who does *actually* copy Metroid 1 and Castlevania 2?

[genquerdeer]

The only distinction that would make sense is that Vania is for game with focus on RPG elements (i.e. numerical statistics that you increment by playing and not just by exploration) and Metroid is for gamnes that don't.

Because let's face it, "Metroidvania" is not actually named after Metroid and Castlevania - it's named specifically after Super Metroid and Castlevania: Symphony of the Night. And SotN being an action RPG is easily it's largest difference from SM.

do you prefer the metroid or vania side of metroidvania

I don't think it's useful to taxonomise them that way. I've never seen anyone produce a definition of what the distinction between "metroid" and "vania" is that didn't end up with at least one actual Metroid or Castlevania game on the "wrong" side of the dividing line, much less one that could fruitfully be applied to the genre as a whole.