David Bowie's surreal opus ★ (pronounced Blackstar) finally arrives this week, and critics are hailing it as an absolute masterpiece. "[It's] one of the most aggressively experimental records the singer has ever made," Rolling Stone's David Fricke wrote. The album certainly isn't without precedent, though, since Bowie has been breaking musical ground ever since he rose to stardom in the late Sixties with "Space Oddity." As we await the release of ★, here are 10 key Bowie tracks that paved the way for this moment.