Hamlet I

Hamlet, quite sensibly, does not immediately leap into action when the apparition of his father commands him to seek vengeance. This indecision would have been vital had Hamlet's uncle been innocent of any sort of treason or murder; however, this is the crux of the play. Within the dialogue of other characters, it is established that many of them believe Hamlet to be insane which would be a detriment to Hamlet's credibility should he seek to recruit for his cause to kill his uncle. He himself is unsure as to the actual guilt of his uncle and must spend part of the play determining it. 

But that's about as much plot as can be foreseen. A straightforward murder story ending in more murder with some love toils with Ophelia thrown in. Frankly, Hamlet's indecision and investigation are the sole reasons the play does not immediately erupt into a bloodbath (ignoring any comments into human psyche scholars have decided stem from Shakespeare's writing).