Based on the context, even if one had never seen the word heinous before, they could assume its meaning. The structure "he was willing to ruin other people's lives to gain power" offers an explanation as to why the villain is being described as heinous.
Other synonyms for the word are abominable, hideous, infamous, and odious.
The only stage direction is for every character to leave, letting Hamlet have his monologue. It allows the reader or listener to relate to Hamlet. It also usually shows exposition in the storyline.
