You may not like this answer, but this is how I've always looked upon Shakespeare's "Romeo and Juliet." I see it as a story about two young people who are both in great need of "falling in love" in order to escape equally unpleasant situations. Both Romeo and Juliet have something to gain from the new relationship and their union is more a running away from rather than a rushing towards. In the end, this view makes their story even more tragic than is popularly supposed.
First Romeo. As the play begins, we learn that Romeo is sick at heart and deeply depressed because the girl he loves, Rosaline, does not love him in return. He goes on and on with his friend, Benvolio, about the matter. He is deparate and sick at heart. He needs so much to have someone to love and to love him back.
As for Juliet, we also know she has a problem. Her father and mother are pressing her into an arranged marriage with Paris. Even Juliet's nurse and confidant is encouraging Juliet to marry him. But Juliet has "not seen the change of fourteen years." How can she be forced into a marriage at such an early age? She sees her parents' convenient arrangements for her as nothing but cruelty. The poor girl is only thirteen years old! How could she be expected to know about life and love?
So, both Romeo and Juliet have a need to escape, and they do so into each other's arms. Oh, how easy it is to mistake mutual negative needs for a true and mature love.
I really don't know why Shakespeare make Juliet fall in love with some one so quickly and plan to get married with him without knowing him much. Did people judge their love only by appearance, since we know both of them are beautiful?