The play's tone (its attitude toward its subject matter and audience) can be hard to pin down and largely depends on a couple of things: 1) how we interpret Richard's character, and 2) whether or not we think Shakespeare is trying to promote the "Tudor myth" – the idea that the Wars of the Roses and King Richard III's reign was one of the darkest periods in English history. Let's break this down.
If you've read King Henry VII's big speech at the end (go to "What's Up With the Ending?" for the 411 on this), then you probably picked up on the play's patriotic tone. Like we've said before, Shakespeare gives his monarch's (Queen Elizabeth I's) grandfather some major props at the end of Richard III. The guy basically swoops in from France and saves England from a tyrannical monarch who's been making everyone miserable for the past five acts. It's an ending that Shakespeare's original audience could really cheer for, because Richmond/Henry VII's victory over Richard was considered the moment that ushered in the Tudor dynasty and a veritable golden age for England.
But what about the rest of the play? Let's face it, Shmoopsters, we may feel compelled to root for Richmond/Henry VII at the end of the play, but overall, Richard has been an entertaining villain. At times we've even admired him for his audacity, his wit, and his evil-genius political moves. What's more, Shakespeare seems to have wanted it that way. At the beginning, Shakespeare practically invites us to kick back, relax, and enjoy the ride Richard takes us on. The fact that Richard addresses us directly (making us his confidants) has a lot to with why we enjoy him.
As the play progresses, though, Richard addresses us less and less, and he crosses a major line when he orders the murders of the young princes in the tower. (Even his wingman, Buckingham, is repulsed by the idea of killing innocent kids.) In other words, Richard's villainy is sort of hilarious at first, which suggests the play has a sense of humor. But then Richard becomes grotesque, which alters the play's tone in a very big way.