Physical appearance is super important in this play. We know this because our protagonist dwells on his physical appearance for a good part of the play's opening speech. Richard has a withered arm and a hunched back, and he generally considers himself ill-formed and ugly.
Richard describes his own deformity and simultaneously tells us that he is "determined to prove a villain," thus equating his physical deformity with his immoral nature. This raises a chicken-and-egg kind of question: Is Richard morally corrupt because he's physically deformed, or is his physical deformity an external reflection of his innate moral underdevelopment?
Richard uses his physical deformity to aid his morally unsavory acts. When he condemns Hastings, he calls up the preposterous claim that he's crippled because of Jane Shore and Elizabeth's spells, even though we all know he's been crippled since birth. Even so, he manages to score some pity points, and no one wants to point out that he's blaming his disability on a false premise.
Richard also hides behind his deformity. When he makes a big show of why he's not worthy of the crown, he mentions his many defects, which make him "unfit for state and majesty." He's deliberately playing the guilt card here, so that everyone will insist that he's equal to his brothers in kingliness, in spite of his physical handicaps. Also, no one will be able to say he's unworthy because of his physical deformity once he's on the throne, since he's already addressed the issue.
Shakespeare's treatment of the players in Richard III is a delicate balancing act. Richard is morally condemnable, and he gets what's coming to him. Still, each character's words sometimes speak louder than his actions, giving us insight into how Shakespeare really regards him. Shakespeare has Richard speak with poetic dexterity, and his brutal actions are often overshadowed by his wit.
By contrast, Shakespeare has Richmond speak like a lofty and noble heroic type. Shakespeare gives "the good guy" some beautiful poetry. Richmond's speech is ethereal, as when he prays before bedtime: "To Thee I do commend my watchful soul / Ere I let fall the windows of mine eyes" (5.3) and often inspiring, as during his pep talk to the troops before battle:
If you do fight in safeguard of your wives,
Your wives shall welcome home the conquerors;
If you do free your children from the sword,
Your children's children quits it in your age.
Then, in the name of God and all these rights,
Advance your standards, draw your willing swords. (5.3)
Basically Richmond speaks the exact opposite of Richard's stealthily intriguing stuff. The fact that he favors Richard with the most sharp and witty of his writing gives us a hint that, though he knows he must condemn Richard in the final act, he's kind of proud of him as a perfectly developed deviant.