Thematically speaking, "Romeo and Juliet" is a drama that is about love overcoming hatred, however, whether the story is more about love or more about hate is open to personal interpretation.
I would actually suggest that the ideas of love and hate hold equality in importance. At its core, the story is about two households who hate one another so deeply, and have for so long, that the reason behind the original rivalry is never fully disclosed. In addition to the hatred shown between members of the Capulet and Montague households, we see two young (and somewhat spoiled) children who essentially show hate-filled disobedience to their own parents. Instead of turning to mom and dad for support, both Romeo and Juliet seek counsel from others (the Friar, the Nurse, and even friends like Mercutio and Benvolio) when it comes to the conflict of falling in love with each other.
Because of love, however, Romeo and Juliet marry. The secrecy that surrounds their marriage results in far more problems in the short term, including the deaths of Tybalt, Mercutio, and Paris, the banishment of Romeo, and ultimately the deaths of Romeo and Juliet.
The end of the story shows that the two households come together in the deaths of their children and end the lengthy feud by errecting memorials in honor of the other's children. However, this is where the story ends. The themes of love and hate weave together so fully throughout, and the story covers such a short span of time, that it is very difficult to say that either love or hate is a more predominant theme. They are both portrayed equally.