I think this game is Castlevania's sci-fi equivalent in terms of impact and there's a reason the term Metroidvania is a portmanteau of the two games. Much like with Vlad's castle, you work your way through the depths of planet Zebes, exploring in a free-form way similar to the original Zelda and Vampire Killer. The music and stark visuals help to highlight the feel of isolation and danger, and even the weapons and item upgrades act as tools to explore further. Just like with Castlevania, I have issues with the precision of the controls which can be frustrating at times, and it doesn't nail the balance between exploration and tedium perfectly, but the achievements here far outweigh the niggles.