Robert Ferrars is a real jerk. There's no two ways about it; he's just incredibly lame. As Lucy says (before she's engaged to him, of course), he's a coxcomb, an arrogant and self-congratulatory lout. There are, as far as we're concerned, no good sides to Robert, except for the fact that he's lucky enough to be Edward's brother, a positive that's utterly lost on him.
Edward and Robert may be brothers, but they couldn't be more different. Robert has none of Edward's good nature or sense of honor; in fact, Robert boasts about the fact that he "stole" the willing Lucy from his brother, then got married in secret. Earlier, he also rejoices in the knowledge that his brother is totally ruined, socially and financially, and takes pleasure in telling Elinor about it. Basically, Robert is a miserable creature through and through, and we think he and Lucy deserve each other.