In the spirit of Halloween, I'll begin with a little tidbit on death. The Duke, under the disguise of a friar, gave quite a lovely speech about death as he tries to persuade Claudio to accept his fate. He says that death is inevitable and life is so miserable anyway, so he's better off with the fate he has. Claudio seems to believe the friar-duke and finds comfort in believing his argument: "To sue to live, I find I seek to die,/ and seeking death, find life: let it come on." (3.1.43-44)
And then Isabella comes in, Claudio learns of Angelo's ultimatum, and we get some typical Shakespearean action. The friar-duke has a long complicated plan that the characters believe is foolproof which can only mean that everything will turn out disastrously.
However, I want to go back to the offer Angelo has given Isabella. There are pros and cons for each character, and I just need to sort them out.
First, Isabella. If she sleeps with Angelo, she can no longer become a nun and her immortal soul is forever stained with the sin of the deed. In refusing the offer, is she being selfish? Or would a sin that saves a brother's life really become a virtue as Claudio says?
Second, Claudio. He has committed a crime according to the law of Vienna and is sentenced to die. Is his sentence just? Claudio and Juliet seemed committed to each other, but were keeping their engagement secret so that Juliet's dowry could increase. He presses Isabella to consider Angelo's offer, as it is his one chance at life. How much love is involved here, and how much greed?
Finally, Angelo. As far as we know, he led a perfectly moral life up till this point and at first was upholding the law without wavering. However, he falls in "love" (which seems more like lust) with Isabella and says that to save her brother, she has to break the law with him. What kind of moral and just character would give those kinds of conditions?
Overall, I think that there is a lot of "seeming" going on. Isabella is seems to be a selfless nun at first, but can be viewed as selfish in regards to her attitude towards saving her brother's life. Claudio seems to be loving towards Juliet, but that love diminishes as we learn that they were keeping their relationship a secret for the sake of money. And Angelo seems to be the most virtuous man ever only to want to break the very law he is publicly upholding.
Each character tries to be good. I think that's what makes this play so hard: there is no defined antagonist and no defined protagonist, and morality is hazy in this play. Here, there is no black or white. We as the readers are simply left with a big GRAY muddle of immorality and virtue.