Hamlet's reluctance to murder Claudius is evident by the end of the scene and rightly so. Personally, I believe that his delay is justified seeing as his direct information on Claudius has come from a ghost, which was often considered an agent of the devil at that time. However, he further justifies this through the mousetrap play, used to watch Claudius` reaction. Therefore, I find it reasonable for Hamlet to have doubt as he says "The spirit I have seen may be a devil (Hamlet, 562)", implying he is unsure of the reliability of the information. In addition, Hamlet wants to ensure that Claudius doesn't go to heaven and is worried that by killing him, Claudius' actions may be forgiven. Therefore, Hamlet does not want to end up being the same person as his uncle, which I find fair yet it also seems that Hamlet is over thinking things and making them more complicated than they need to be. This is also something Shakespeare portrays in Hamlet throughout the play. Despite all of this, I think that it is Hamlet's nature that delays him from killing his uncle as he is a sensitive young man who shows little 'killer instinct' despite his anger. Overall, I believe that these are the combination of factors that encourage Hamlet's delay and enable Shakespeare to show the audience these aspects of his character.
In addition, I found this interesting video on how Hamlet`s delay translates to the modern day, and how the themes portrayed have remained relevant today.
http://www.youtube.com/watch?v=S4DQhTzmjRM