How others will see it. Many viewers haven't seen the play, very few will have seen the 1948 movie, and fewer still will recognize that this prior production is vastly superior. Most who see this film will appreciate the dose of Shakespearean culture, the star-studded cast, and the craftsmanship of its filming.
How I felt about it. It's not very good. It lacks the majesty of Laurence Olivier's version, directed by a confident stage veteran (Olivier, of course) who best understood the play as it was intended by Shakespeare.
I don't begrudge the casting. Gibson is as good a choice as any for the lead, especially when box office draw is to be considered. Zefferelli earned the right to attempt his own filming of Hamlet with his Romeo and Juliet (1968), a delightful effort.
Perhaps the biggest difference between those two films is the repute of the cast. Romeo and Juliet had a young no-name roster of actors. Michael York later became famous, but he was just another pretty face at the time. The energy of the young cast as they sank into their characters differs from the experienced and more wary posings of the actors in Hamlet. Ian Holm, in particular, plays the fool, mugging it up, and tagging after his leaving son like a dog following his master, making the sparkling advice, "Never a borrower, nor a lender be," sound like "Don't drink the water, and be sure to wear a condom."
Some of the plotting weaknesses of the original play become apparent in this handsome but lackluster adaptation. Hamlet is the tragedy to top all tragedies, and one wonders if Horatio becomes the next king, since he is the only person left standing who does more than wear an uncomfortably hot rented costume. Ophelia (Helena Bonham Carter) goes mad, perhaps because Hamlet said oddball things to her before sailing to England, though that is no good reason at all for her subsequent behavior.
At any rate, the only advantage that Zefferelli's Hamlet has over the magnificent Olivier production is that the more recent incarnation is in color and has all your favorite non-American English speaking actors. But Olivier knew that the play is the thing. The lines are not there to flesh out the scenes, rather, the scenes exist to utter the magical lines.