Sadly Nightmare Sphere 0 was never completed (or was it just lacking a save system ?). This one was very good, alas a little confusing at times on what to do, where to go. Has 5 endings if i recall correctly, depending on soul meter and status.
As for the metroidvania term, honestly i always jump to the conclusion of "The most popular thing will be the name of the genre". Metroidlike becomming metroidvania (recently heard IGAvania for all games created by IGA that are metroidlike), Wolfenstein being overshadowed by doom for doomlike (Then again call of duty-like is also a thing), Soulslike (when the concept of cryptic progression was allready introduced in the king's field series, or if you want to be a nerd, was allready a thing on tower of druaga on arcade).
Goonervania was a funny term to read, kudos.