Have you ever sat and watched the Spanish channel, not understanding anything that is being said? I have. You get so caught up in the actions you don't even realize you don't know the language, but you follow the plot quite easily. You can almost swear you know what they are saying, even if you only catch every tenth word or so. If I asked you to read a book written mostly in Spanish except for every tenth word (and you don't know Spanish, of course) you wouldn't have a clue what was going on and would lose interest rather quickly. The same may happen for Shakespeare. I believe there are many advantages of watching the movie of Romeo and Juliet over interpreting the book.
Body language and voice tones are a major factor in determining a character's traits. In Act II, the scene in which Mercutio is teasing the Nurse was quite the opposite if how I had imagined the scene while reading the book. I had expected Mercutio to be pacing and randomly saying his speech making fun of the Nurse, acting more sophisticated than her. I never thought he would be hopping and dancing around her, yelling things at her and harassing her. Everything seems to come together when it is put into actions.
Reading an unfamiliar language can be monotonous and meaningless. In the movie, lengthy speeches come to life and don't seem so dragged out. There are short with little actions in the video that would take five plus lines to show verbally. The video gives you a better sense of what you are reading and an easier way to interpret the Elizabethan language. .
Although a challenging book improves your language skills, the movie of Romeo and Juliet familiarizes you with the characters. Reading a play doesn't identify their true personalities as well as the movie, and you can tell what they are thinking without any verbal explanation. While reading the book, I pictured the first two scenes to be very serious and dramatic.