Warning: If you read this post the ending of Interstellar will be spoiled for you and you may see no point in watching it. You should probably bail if you haven't watched the movie already.
If you were confused by the ending of Interstellar you may find Jonathan Nolan's original ending more satisfying. There's a tradeoff, though: it's much more depressing. He revealed his initial plans at a Q&A for the film.
As you may recall, Cooper (Matthew McConaughey) enters a five-dimensional realm inside of a black hole and is able to send out the data to solve Brand's equation in Morse code before escaping. But in the original script there wouldn't have been five dimensions, and the worm hole would have closed while Cooper was sending the data, leaving him trapped inside. Christopher Nolan changed the ending when he came onboard as director. Jonathan didn't say, however, if the data would have made it out.
The takeaway from this is Christopher is the more sunny of the Nolan brothers.