The first Metroid scared the crap out of me as a kid. The haunting atmosphere along with the creepy music made it an unforgetable experience. But it was positive scary and it fascinated me. Taking the elevator down to kraids lair for the first time and hearing the iconic melody is something you will never forget. It always plays in my head.
When I played this as a kid, I had no guides, it was played totally blind. So I had no idea what waited around the corner. I tried to draw handmade maps, but I thought the level design was so complex at the time that I always lost track.
Most other Metroid games has great atmosphere as well, but first one has special place in my heart since it played like no other game at the time.