Going into act III many people were saying that they got the perception that Queen Gertrude was aware of what Claudius has done, but after reading act III I'm not getting that vibe. Based on my perception, when Hamlet confessed to his mother about what he knew of his father's murder she seemed shocked. She even then gave off the portrayal that she didn't believe his story and blamed such outrage on his "madness."
Polonius's murder did not come as a shock to me, I expected it. I also saw Claudius's reaction to the play coming. What I didn't understand was Hamlet's actions toward Ophilia during the play. At one point he was laying in her lap and at another he was "shunning her to a nunnery."
My favorite part of the act was when King Claudius was repenting his sins and Hamlet came in and almost killed him. Hamlet stopped himself because he didn't want Claudius to be able to go heaven, but as soon as Hamlet leaves the room Claudius says, "My words fly up, my thoughts remain below: Words without thoughts never to heaven go." Which gives the audience that engaging feel of regret that Hamlet didn't kill him when he had the chance.