As somebody that loves spaghetti western soundtracks, it's been very interesting to actually watch the movies. I hadn't seen any of the Leone films until very recently!
As much as I love the music of the "Dollars" trilogy, they didn't fit into the movies like I imagined at all. Though they still elevated the movies.
Once Upon a Time in the West and Duck, You Sucker are absolutely amazing in how they use the music. And just amazing in general.