The chief complaints against Polanski's version is excessive, unnecessary violence and gratuitous nudity.
Here is an excerpted review by Glenn Erikson of the 1971 film:
About the best the critics could muster for Macbeth was to grudgingly chart Polanski's alterations to the bard. "Lady Macbeth walks around in the nude", was about all one heard, as if the movie had tried to turn Shakespeare into Oh Calcutta!, or Hair. Theater critics normally enjoy debating alterations and edits done to the famous texts, as improvements or interpretations, but in film, even Laurence Olivier was clobbered for daring to cut scenes from his 1948 Hamlet. Orson Welles? He was always considered untouchable-crazy anyway, so the radical reshaping in his movie versions were indulged or praised as inspired creativity.
Not so Roman Polanski. Here was a play with bloody mayhem in practically every scene or alluded to as taking place offstage, and he dares to bring it front and center. There's been a battle, so he shows wounded, bloody men. There's a party, so we see a cruel bear-baiting scene, also very bloody. The fights (excellently arranged by William Hobbs) really look like people are hacking each other to bits. The blood and guts made reviewers acutely aware that, two years after his wife Sharon Tate was murdered in the most lurid and bizarre crime of the century, Polanski seemed to be wallowing in gore. The 'home invasion' rape and slaughter of the Macduff household plays as a creepy shadow of the Tate killings, complete with bloodied, murdered children.
In contrast and just seven years later, (1978) Trevor Nunn de-emphsises the gorey aspects and returns more dignity to the Bard's work. His emphasis lies in appreciating the grace and nuances of the poetry. Here is an excerpt of a review by film critic John Murphy:
Through his actors, Nunn preys on the audience’s imagination. Instead of spoon-feeding us a steady, predictable diet of horror show gore and carnage, Nunn emphasizes the imagistic poetry of Shakespeare’s language. The language, channeled through such superior interpreters as McKellen and Dench, takes on an expressionistic life of its own. “Full of scorpions is my mind,” Macbeth confesses to his wife. The horror is internal, not external, and Shakespeare’s words have a terrifying immediacy that only the imagination can do justice. I felt a chill down my spine as Macbeth says, “Light thickens, and the crow makes wing to the rooky wood. Good things of day begin to droop and drowse, whilst night’s black agents to their prey do rouse.” The barren set, then, is a mindscape, a blank canvas on which the audience paints its own fears.