Wow. All this lack of love for the original Metroid breaks my heart. Sure in many ways, it doesn't hold up, but not many early NES games do.
I still remember going over to a friend's house who got them game when it came out; when I realized the depth of this game, my mind was blown; of course, I was a pretty young kid at the time. Being raised I had never seen anything like it.
My parents hated that game, though. When I got my own NES and started playing at home, they were annoyed by the repetitive music. And, they kept asking me questions about it.
Parents: "Why is that guy running around naked?"
Me: "He's NOT naked!"
I guess they thought the yellow was more of a flesh tone? I didn't know at the time that Samus was a woman. I don't know that particular revelation would have gone over well, anyway.
Castlevania sounds great!