I remember watching a series "retrospective" on Metroid, many years ago, by Game Trailers. I think they effectively summarized why that series, and extension parts of Castlevania, were so successful. In short, it was pointed out how Metroid combined platforming elements from Mario, along with the tool-driven adventure that Zelda wielded. I think that Castlevania really uses that to their advantage too. Paves the way for many other innovations and gameplay flavours on top of that :)







