Quite the heated discussion about something as mundane as Castlevania nomenclature.
Personally, I've never liked the "Metroidvania" term. It feels too derivative: I'd like to think of Castlevania as its own unique genre, and less as a stolen idea from another game... I've forced myself to use "Symphovania" when I write -- it sounds absolutely ridiculous, but it does the job.
And ultimately, that's all that's really important: it doesn't matter if you write "castleroid" or "GOWvania", as long as you're understood.
And for the record: how about: "Castlevania"?