What is the difference between “I just love that movie” and “I love that movie”?

In terms of meaning, the first sentence is much stronger than the second. The word “just” is used to emphasise the fact that you “love” the movie very much. It’s another way of saying, “I simply/really love that movie”. “Just” is often used in speech to mean “there is no other word for it”.
 *The young heroine in the new movie was just beautiful.
 Source:  ‘Know Your English’ Series – The Hindu Daily, August 22 , 2005.