How does Shakespeare craft (Act 1, Scene 1) for dramatic impact?

The first scene of the play, like most every scene of the play, is very well known, and very puzzling. Without explaining his reasons in detail, T.S. Eliot once declared the first lines of the play to be the best lines in English. He and many other critics have found this scene to be a microcosm of the whole play, as it were. Shakespeare uses many deceptively simple rhetorical tricks to introduce some of the major themes and concerns that he follows through to the play’s end.

For example, in a play that contains many of the most famous, most unanswerable questions ever expressed, whether literal questions (“To be or not to be”) or interpretive questions of motivation (“Why doesn’t Hamlet just kill Claudius straight away?”), it is remarkable that Shakespeare begins Hamlet with a question, “Who’s there?” Who’s there, indeed.... On one level, this is a simple question, one that is asked every day in the most innocuous contexts. But on a deeper level (and everything in this play is richly rewarding on a deeper level) it is one of the basic questions of philosophy. Who is there? Who are we? What is man? Who is Hamlet? What is Hamlet? In this most philosophical of plays, we begin with a moment of covert philosophy, a question simple on the surface, but profound when pressed; and the first scene continues this focus on questioning, giving us question after question. Horatio, the quintessential scholar, skeptical and empirical, begins by questioning the reality of the ghost; eventually, he is exhorted to “question” the ghost in a more literal way – to ask the ghost questions. In general, then, the first scene takes us from the no-nonsense world outside the theater, the world of Horatio and his doubts, to the magical, metaphysical, ultra-theatrical world of Hamlet. We may bring certainties to the play, but we are encouraged almost immediately to abandon them.

Thus before we have even seen Hamlet (the younger Hamlet, that is) we are deeply mired in the play’s dubious, spectral atmosphere.