Anti-Semitism makes The Merchant of Venice one of Shakespeare's more troublesome plays for modern audiences. Even were that not an issue, the seriousness of the Shylock/Antonio plotline with its infamous pound of flesh feels seriously at odds with the romantic escapades of the other characters; it's hard to make that piece fit into what is, after all, classified as one of Shakespeare's comedies.
(Yeah, I know, "comedy" in the Shakespearean sense doesn't mean quite the same thing as it does now, but even so, it generally means that the play will be relatively light in tone with happy endings for nearly everyone. My college Shakespeare prof summed up the distinction as "If everyone ends up dead, it's a tragedy; if everyone ends up married, it's a comedy.")
Michael Radford's new film adaptation opens with a few screens of text that provide some historical context about the treatment of Jews in 16th-century Venice, and Radford's screenplay condenses the play a bit, cutting principally (I think; it's been a while since I read the play) from the romantic capers; this version of Merchant is definitely more drama than comedy.
Al Pacino stars as Shylock, and given his ever-increasing penchant for hamminess and bellowing, it's a pleasant surprise that this is a relatively quiet and understated performance; only in the "Hath not a Jew eyes" speech does he get at all loud, and even that is entirely in keeping with the rest of his characterization.
He is particularly good in the courtroom scene, capturing Shylock's stubbornness, as well as the sense of grief and betrayal that motivates it. Jeremy Irons as Antonio is also very good in this scene; sadly, Lynn Collins's Portia does not come off as well, and even by the lax standards of Shakespearean cross-dressers, her Balthasar is painfully unconvincing.
The pruning of the romantic plots, and the shift in tone towards drama, makes what's left of those romantic plots play a bit more heavily than they probably should. When the four principal lovers have their argument about rings and promises, it comes off not as fluffy comedy, but as a cruel lie on the part of the women.
The Shakespearean blank verse is quite easily understood here; the actors deliver it in such a way that even when we don't follow every word and sentence, the gist of the action is abundantly clear. It's a solid production of the play, and an entertaining movie