I'm a huge fan of Gershwin's opera Porgy & Bess -- such a huge fan that I generally don't even like tunes being excerpted by jazz musicians (there are exceptions, like Sidney Bechet's or Pete Fountain's renditions of "Summertime", but I'm really picky). The biggest exception for me is the album that Miles Davis recorded in 1958, featuring his ground breaking trumpet interpretations over Gil Evans's arrangements. The record is like a modern jazz opera in itself, equally satisfying as the original (at least to me). As a wind player, considering what Miles does on his horn, it's also endlessly inspiring.
This musical prayer to the Physician of Souls is a high point for me, though the whole album is worth countless listenings. Stay safe everyone, and God Bless you.
[ This is not a comprehensive list, nor is it representative of the "most important" or "best." Instead, following Duke Ellington's adage that the greatest music and musicians are "beyond category", I'm starting 2020 by sharing 100 jazz tunes I feel everyone should have the chance to hear--really just tunes and performances that I love. ]