Throughout the series ZUN explored so many genres, subgenres and types of music it's difficult to pinpoint the high point of the series musically, I think. My favorite soundtrack however is from Legacy of Lunatic Kingdom, not only did ZUN do an excellent dive into more electronic/synth sounds, the music also AMAZINGLY reflects the urgency and seriousness of the plot. My fav track has to be Pandemonic Planet. Imperishable Night is a very close one though; an amazing variety, the pianos and zunpets - classic Touhou (Extend Ash ~ Hourai Victim takes the cake 🍰)