how would shakespeare's audiences have reacted to the play?

Since we'll never know for certain how the audiences would have acted seeing the play we have to examine the history and cultural norms surrounding the Elizabethan time period.

Most people during this time period did in fact believe in witches so the audience's reaction to the opening scene and subsequent scenes with the witches were, most likely, taken very seriously. The audience would have reacted more emotionally than audiences do today to the witches on stage. They also would have contemplated what was being said by the witches much more closely. The concept of Evil was a very intellectual topic during this time period. The audience would be frightened and intrigued to see Evil manifested physically on stage by the witches.