As Herbie Hancock says in the mini-documentary below:
Here's a record that I could recommend to anyone--from any country, of any age. If you want to hear the spirit of jazz, listen to Kind of Blue.
And here's the first part of a BBC documentary entitled "1959: The Year That Changed Jazz":
Update: Fred Kaplan explains the album's greatness. HT: Z
There's also a book on the making of the masterpiece, though I haven't yet seen the book and don't know how good it is.