We expect Romeo, being the eponym and hero, to be the character of central focus throughout the play. However, at times, Mercutio seems more interesting to the audience and draws the focus away from Romeo. His death and its consequences shift the focus back on to Romeo and Juliet. This may have been intentional, on Shakespeare's part.
Benvolio presents Romeo as one who keeps to himself as he is alone but for his love for Rosaline. In fact, Romeo "gladly flew from" Benvolio as he approached. It is his love-sickness that is made apparent by Romeo himself and even he admits, "This is not Romeo". He is softened by his infatuation with Rosaline. He speaks poetically and romantically of her but appears less poetic than pathetic, to the audience.
"... she'll not be hit
With Cupid's arrow, she hath Dian's wit:"
However, Romeo expresses confusion with many oxymora.
He cries, "O brawling love, O loving hate", for example. This is comparable to Juliet's similar oxymora, after she hears of Romeo's killing of Tybalt. For example, she cries:
"A damned saint, an honourable villain:"
Many observe that Romeo is in love with love itself. Indeed, he always appears caught up in it and rarely acts admirably as a result. While he exclaims that love is "brawling" and later that "it is too rough", he seems to always be deep in love and passion. He goes from infatuation with Rosaline...
"From love's weak childish bow she lives uncharm'd"
... to passionate love of Juliet,
"For I ne'er saw true beauty till this night."
We first meet Mercutio in the 4th scene. His cynicism is immediately made apparent by his suggestion to Romeo, to "borrow Cupid's wings". He continues, a little later, with his Queen Mab Speech. He begins with...