These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
And a lot of these are double albums which are long even by double album standards; Get Up with It exceeds two hours, a running time almost unheard of in the vinyl era. Then there's all the extra bonus tracks on the CD versions which further add to the amount of material waiting to be explored; for an extreme example, the CD reissue of Big Fun had about 50% more material than the vinyl version.
Even if you say, "Okay, I'll just start out with the albums that got five-star reviews on AllMusic", good luck. Counting box sets and compilations, there are thirty-five of them as of May 28, 2013 (although some of these are just repackagings of previous releases).
Broken Base: Hard to avoid when you're considered the poster child of each new jazz movement. Will it be hard bop, cool jazz, modal jazz or fusion? Acoustic or electric? The first great quintet or the second? Before or after he incorporated rock, funk, Indian sounds or even synthesizers? Some critics still won't forgive him for putting out Bitches Brew, the Woodstock-inspired jazz orgy of a record that inspired, above other things, Radiohead's OK Computer.
Growing the Beard: When he was playing frenetic bebop music, he sounded uncomfortable. Once he became a bandleader and had the freedom to play in his unique style he became, well, Miles Davis.
Magnum Opus: The most frequent ones you'll hear mentioned are Kind of Blue and Bitches Brew.
Also, The Birth of the Cool. To a lesser extent, the Gil Evans collaborations and the entire output of the two "classic" quintets: the one with Sonny Rollins that recorded for Prestige in the 1950s, and the one with Herbie Hancock and Wayne Shorter that recorded for Columbia in the 1960s.
You're sure to find a fan that can come up with a decent justification for naming any of his works as his magnum opus. Some go so far as to narrow down a single trumpet solo.
Miles Davis: If you understood everything I said, you'd be me.
Vindicated by History: His funk-influenced 1972 album On the Corner was critically panned and a commercial failure upon its release. Now it's recognized as a huge influence in the development of hip-hop, electro and drum and bass, as well as being one of his best albums.
His 1974 album Big Fun received the same treatment, though it was more a case of being ignored than being reviled. Four ~25-minute songs coming out at the start of the disco era will do that to you. On the Corner inspired vitriolic hatred because jazz purists saw Miles' increasing use of tape editing and rock/funk influences (including the use of electric instruments) as ruining jazz purity. His wont for On the Corner to be mastered for AM radio fidelity simply so kids would hear his new album and get back into listening to him instead of James Brown was the last straw for some fans.
Taking a broader view, the fusion era in general as a whole could be seen as this; at the time Miles and Teo Macero's editing of performances on these records was very controversial and alienated jazz purists, but the albums are now usually recognised as masterpieces.