In terms of chords and melody, Castlevania - Vampire Killer is more complex than the typical song, having above average scores in Chord Complexity, Melodic Complexity, Chord-Melody Tension and Chord-Bass Melody.
Castlevania - Vampire Killer is written in the key of D Minor. According to the Theorytab database, it is the 4th most popular key among Minor keys and the 10th most popular among all keys. Minor keys, along with major keys, are a common choice for popular music. The three most important chords, built off the 1st, 4th and 5th scale degrees are all minor chords (D minor, G minor, and A minor). See the D Minor Cheat Sheet for popular chords, chord progressions, downloadable midi files and more!