Aside from a few grand sets and a Portia so luminous she could have been peeled fresh from a Botticelli, Michael Radford’s new film “The Merchant of Venice” is merely passable Shakespeare.

Darkness lurks under the romantic plot. Bassanio (Joseph Fiennes) falls in love with the beautiful, and rich, Portia (Lynn Collins) who lives in her own island mansion outside of Venice. Intrigued by her assets, he cannot seduce her without borrowing money from his older gay lover Antonio (Jeremy Irons, adding another notch to his illustrious career of playing over-the-hill, frustrated homosexuals). Antonio, in turn, has to borrow the money from the usurer Shylock (Al Pacino), who will charge him a pound of his own flesh if the debt is not paid. Bassanio arrives at Portia’s only to find out that he must solve a riddle instituted by her dead father to win her. In the meantime, Shylock’s daughter Jessica (Zuleikha Robinson) runs away with one of Bassanio’s friends, and her poor father becomes incensed, demanding his deadly payment from Antonio.

At least, that’s how it goes in the movie.

Radford’s omissions from Shakespeare’s text are disappointing. Inexplicably, he neuters the wonderful wordplay of the fool Lancelot (Mackenzie Crook), leaving him as a boring space-filler. Much worse, this politically correct “Merchant” mutes Portia’s critique of her German suitors, and expends three opening screens describing the poor treatment of Venice’s Hebrews.

The film dotes upon Shylock, which wouldn’t be such a blunder if the leading man could stretch to fit the enlarged persona. Overly concerned with sympathetically portraying Shakespeare’s “evil” Jew, Pacino tones the character down to a shuffling whiner. This odd choice rubs against all the surrounding Venetians, who continue to treat Shylock as the villain of the Shakespearian text.

As a result, Pacino is out of step with the rest of the movie. And though he maintains a comparably calm state throughout, he still sporadically goes over the top. Uttered with a heavy Jewish accent that sounds vaguely surreal, his sobs of “Jessica, Jessica!” fail to garner either sympathy or hate, instead calling to mind another showy sap in a similar situation: Roger Rabbit.

A serious drama barely masquerading as a comedy, “The Merchant of Venice,” depends entirely on its actors to lead it safely to success. Ideally, the ensemble of skilled men and women tease the contradictions from their parts through bold decisions. But, consumed with the problem of Shylock, Radford ignores the other characters. Consequently, several nagging issues mar their somewhat good performances.

Tied down and held captive to her dead father’s wishes, Portia is an emblem of powerlessness who eagerly receives clout when she masquerades as a man. Yet Collins plays her carefree and in charge all the way through; her motivation for dressing up is eradicated through this misguided portrayal. In addition, her courtroom appearance, while riveting, is riddled with a sloppy cruelty untethered to her character development. Stronger direction could easily have connected the loose strands.

Equally problematic, Shylock’s humane behavior towards Jessica makes her pivotal flight from her father inexplicable, leaving Robinson to flounder, her acting adrift somewhere between confused and pathetic.

In fact, murkiness permeates most of the performances. Besides Pacino, the actors fail to make significant choices, and flatly deliver their lines, leaving the problematic ending devoid of any enlightenment. You might as well just read the play.

Drenched in mist and atmosphere, the well designed sets are the film’s sole saving grace. They are neither period nor modern, but engender a imaginary world inspired by Renaissance painting. They hint at a Venice deeper than Radford’s, where complicated spirits struggle for hard answers.

Shakespearean adaptations are a rare chance to showcase acting. Good performances go beyond a simple recitation; they are critical readings of the text themselves, offering insight into the meaning behind the rich language. But when all is said and done, this “Merchant of Venice” functions merely as a reading of the play, not a performance.