I think when the author is able to provide a window to the inner soul of the main character(s) and we find a character who not only needs to love and be loved, but who can also deeply empathize with the struggles and turmoil other characters are going through. This character(s) becomes even more dynamic as he/she strives to shield or protect another character from pain.
Loving and wanting to be loved is not enough to make a great character. We all want those things. But a character with empathy, a character who deeply cares about someone or something is a character with depth, with dignity, honor, and perhaps even some class. If this character takes personal risks, allows him/herself to get injured in some way, hurt, scorned, humiliated to shield the one he/she is protecting, then the characterization becomes even more dynamic and riveting. There is sacrifice. This character stands for something and stands out, a cut above the usual crowd.