Interstellar and the end of the film era
Today, nearly all movie theaters have converted their projectors to fully digital systems. Although movie theater 4K (4096 x 2160) is a little higher resolution than consumer TV 4K (3840 x 2160) - and definitely an improvement over standard HD (1920 x 1080) - nothing can match the resolution and shear awesomeness of 70mm IMAX film projection. Christopher Nolan is one of the last true film holdouts and with his new movie Interstellar, is pushing for the full "film only" versions to be shown across IMAX theaters.Bottom line: this is one movie you probably want to see in the theater. Otherwise you won't get to see its true glory until 30 years from now when the industry starts selling 32K resolution digital TVs.
Film running through a projector is tricky. The film, as a whole, must keep moving, obviously. But 24 times per second, the film directly in front of the lamp will stop, the shutter will open, and the image will be projected to the screen. This introduces a little bit of jitter that would be technically feasible to do on digital, but no sane person would implement that because it would be "degrading" the presentation of the movie. A good projector introduces very little jitter, but it's still there, and when you remove it (because it's all digital) it dilutes some of the ambiance of the movie. Add in little bits of dust or scratches, which occur even on a brand new print, and those are even harder to realistically replicate in digital, since you want them to be mostly imperceptible, since you rarely notice them directly, but you do notice their absence.
A lot of this might have to do with what "feels" right based on "how we used to do it when I was a kid!" But you know what, who's to say that's wrong? Digital is great for a lot of things, but when telling a story to beings living in an inherently analog world, sometimes having the story be told *perfectly* actually makes the story less engaging, since it doesn't feel "real'.