Here's a cool little nugget from Castlevania producer and all-around wizard Koji Igarashi:
"I was actually surprised by the name [Metroidvania]. In my heart, I really wanted to create a Legend of Zelda style game. But I suppose that when you turn Zelda into a 2D platformer, yes, it resembles Metroid."
Source: http://www.usgamer.net/articles/gdc-2014-why-koji-igarashi-is-grateful-for-the-word-metroidvania