Doing It for the Art: Despite many studios pushing for digital cinematography, Christopher Nolan's preference for film stock still prevailed. Interstellar could very well be the last IMAX film projected on 70mm prints, due to the rapid conversion to digital the company has been going through.
Playing Against Type: Matt Damon typically plays heroic characters. Here, he plays a cowardly antagonist who wants to leave Cooper and his friends to death. Examined here in this article (spoilers herein).
Steven Spielberg was originally attached to direct under the first script written by Jonathan Nolan. This makes certain twists in the third act make a lot more sense.
The original version had more humor, and featured the NSA (not NASA, the NSA) forcing the space mission. In addition, the time travel at the end was to be much, much more complex. There was also a a bunch things changed from the original script, such as:
Murph was supposed to be a boy.
We would've seen a young Dr. Brandt finding the wormhole in the film's original cold open.
Chinese astronauts as antagonists. They reach the planets before Cooper and his team does.
Amelia and Cooper falling in love.
The original script suggested that TARS and CASE were more humanoid robots instead of the blocks we see in the film.
Bill Irwin also provided the voice for CASE in addition to TARS, but was latter replaced by Josh Stewart.