As I started reading, I had some trouble sorting out what was a theme in the play, what might become a theme, and what was forgettable in terms of a theme. I've read the first act and I'm working though act 2 right now, so it's hard to say right off what a theme might end up being. It could go a bunch of different ways.

I can potentially see a necessity for revenge coming up as a theme. After the scene with the Ghost, everyone is swearing to everyone, and Hamlet agrees to avenge his wronged father. How that will effect the audience? Well, it probably makes them expect Hamlet to attempt to kill the Uncle. However, I doubt this theme will make them feel that they too can kill their uncles. They might begin to sympathize with Hamlet and understand why he feels he must kill his uncle. What does the theme of revenge mean? It means in some cases, people can feel very strongly that they must take justice in their own hands and see it though.

Although not as much yet, I can see a theme of hopelessness leading to death/suicide. Hamlet's situation is pretty grim from the start. His dad dies and then his stinkin' uncle comes in within a couple months and marries his mom. To top that all off, he finds out he has to kill him because he promised a ghost he would. There's a great line in Act 1 where Hamlet is being beckoned by the ghost but the guys are holding him back. Finally he says, "Why, what should be the fear? I do not set my life at a pin's fee." I might be reading this wrong, but he's kinda saying, my life sucks anyway, who cares if the ghost ends up killing me (or whatever ghosts do to people). So I can see hopelessness connected to death becoming big. And this helps shape it into the tragedy it is.