To start answering this question, approach it from two ends. First, think about what you think is "great and wondrous about love." Second, examine how the young lovers display, embody, articulate, or otherwise enact realities about love. You could start with either one of those, by the way. You could start by cataloging how the lovers act. Act I, they show devotion—they leave the city when their love is forbidden, they defy parents, etc. Later in the play, they are extremely fickle, shallow and abusive.
You'd then compare that to the key elements of love. What do you think is great about love? What are its defining components? Passion? Faithfulness? Desire? Statements of love?
The lovers have some of these, but not others, and so that would lead me to the argument that they don't display very much that is great or wondrous about love. I'd then cluster the support for this, either lover by lover, or, more likely, concept by concept.