Romeo is moody, immature, and impulsive as the story begins. He is also sensitive and compassionate though. As the story continues, Romeo matures somewhat, but maintains these basic characteristics.
Romeo’s sensitivity and compassion, as well as his brooding, moody nature, is evident from the very beginning when he sees the aftermath of the brawl.
What fray was here?
Yet tell me not, for I have heard it all.
Here's much to do with hate, but more with love.
Why then, O brawling love! O loving hate! (Act 1, Scene 1)
While this compassion is generally a positive trait, it is also Romeo’s undoing when combined with his other traits—impulsiveness and immaturity. When he interferes in the sword-fight between Mercuito and Tybalt, he causes Mercutio’s death and his own banishment.
At the end of the play, Romeo really has not changed and learned much. He still risks his life to return to the city, and impulsively kills himself when he thinks Juliet is dead. While he is a bit more mature for having been banished, he still returns when he shouldn’t. His rash actions cause Juliet's real death.