] All the video versions of this play answer this question differently. The most extreme answer to this question I have found so far is in the Nichol Williamson verion where Hamlet is completely and utterly wacko from the time he sees the ghost to the end.

I really dislike the Nicol Williamson version of Hamlet. I think removes any subtly or ambiguity from the play, which is what makes it a great work of literature. Blech.

Regarding how mad Hamlet is, I think he is in his right mind throughout the entire play.

He has moments when he loses his temper/composure/balance: after the ghost leaves and he talks to Horatio and the others, when he talks to Ophelia about nunneries, when he talks to his mother in her chamber and kills Polonius, when he leaps into Ophelia's grave, and when he kills Claudius.

The fact that he's killing people or wounding them mentally by some of his actions certainly crosses the line of what we would call mentally stable today. But I 0personally believe that Shakespeare wrote him to be not mad.
] For me, esp. after this group read, I believe that Hamlet is more or less in his right mind until he gets confirmation of Claudius evil deed. At which point he gets somewhat carried away with his revenge and has a hard time controlling his passions. I think I would have to say that I don't think he ever goes completely off his rocker. He is too much of a thinker for that.

] Any other thoughts?