I've Seen That Face Before (Libertango) has higher complexity than the average song in terms Chord Complexity and Melodic Complexity.
I've Seen That Face Before (Libertango) is written in the key of A Minor. According to the Theorytab database, it is the most popular key among Minor keys and the 7th 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 (A minor, D minor, and E minor). See the A Minor Cheat Sheet for popular chords, chord progressions, downloadable midi files and more!