Poses many important questions> A few will be answered, but most will remain open to interpretation. Is the ghost genuinely the spirit of Hamlet's father or an evil spirit sent to trap him? Is it telling the truth in claiming Claudius is a murderer? Does Hamlet love Ophelia? Will Fortinbras invade? Just what is rotten in the state of Denmark?
The acts neds with Hamlet seemingly convinved that the ghost is in truth his father's spirit, even though it has offered him no comfort. Hamlet accepts the ghosts orders to take revenge on Claudius, but, Act One has already revealed Hamlet's questioning mind, that he seeks the truth behind appearances. The uncertainties that he feels, particularly the suspicion that the ghost may be false, will resurface to hamper his speedy vengeneance.
That theme of deceptive appearance recurs throughout the act, and is expressed in the sentence Hamlet writes about Claudius in his notebook: 'That one may smile, and smile, and be a villain'. But in Sc2, Hamlet's own preference for reality over appearance ('I know not seems') stands in ironic contrasts to his intentions in Sc5 'To put an antic disposition on': to pretend to be mad.