Dryden, in his essay "Absalom and Achitophel," claims, "Great wits are sure to madness near allied." Is Hamlet's wit so above others intellectually that it drives him to real madness even as he feigns insanity?
Consider Einstein. Don't you have to be a little "mad" in order to be a visionary, to see beyond the "real" world? That said, I don't know that Hamlet falls into this category. The stress of grief, and of knowledge unshared, the inability to come to a decision - these are the issues that plague him and cause such fretfulness of feeling.
I do agree that madness and 'great wits' are very close. Those who have great wit can comprehend things and reason on levels that the masses cannot so they often appear 'mad'. Also, some times those who are classified as insane have simply just done away with the normal protocols, rules, and structures of human or societal interaction. Hamlet falls into this category - his mother and uncle have done away with normal societal regulations why shouldn't he? But I don't believe he actually is insane - his actions are too logical at points and his words too pointed.
Very interesting...I have always heard that there is an extremely fine line between insanity and genius. Perhaps it is true for Hamlet, but I don't think so. He is very witty, and even in his feigned madness, I believe, he is also in total control. I like to look at his actions as a very complicated chess game. Only with the last scene in Act V does he lie down and die without much fight (considering Claudius is also dead by now) since his job is essentially finished.
This is, and has been, my favorite over the last 20 years, probably since I'm unsure which side I favor most.
That said, one key observation I've come across in that time is the contrast between the oft mis-quoted "Genius" instead of "Great wit". The first is the latter, effectively applied - as Dryden did and most likely meant to imply. Thus, I translate the quote closer to "Smart and crazy are kissing cousins".
This is not a pedantic distinction - Consider the more familiar Franklin mis-quote of "Those who would trade freedom for security deserve neither". In fact, the accurate paraphrase is closer to "Those who would trade essential freedom for temporary safety deserve neither". The latter is intuitive, given Franklin's preeminent role in trading some freedoms for some safeties in the U.S. Constitution.
Applied to Hamlet, if fading memory serves, his behavior is less insane than amoral, in that he is a capable actor confronted with the burden of creating a morality without the benefit of social consensus. (But then, it's been 25 years since I read the play. YMMV)