For the most part, the 1993 film directed by Kenneth Branagh very accurately portrays the Shakespeare play. However, there are some differences in terms of lines delivered and characterization.
Many lines were deducted from the original Shakespearean script, which we can especially see in the opening scene with respect to Beatrice's lines. In particular, lines 32-35 have been cut out as well as 41-43. Instead, Beatrice begins her speech scorning Benedick by asking how many men Benedick has killed, implying that she thinks he is a useless fighter. Also, Beatrice's final remark aimed at scorning Benedick before he arrives on scene is, "He is no less than a stuffed man" with the line, "[B]ut for the stuffing--well, we are all mortal" having been removed as well (I.i.48-49). For the most part, the choice to remove some of Beatrice's lines was made with the intent of making this scene more amusing and easier to understand. Even some scholars are still very unclear about Beatrice's meaning in some of her earlier lines.
Later in the film, another interesting choice to remove lines can be seen in Claudio's reaction at Borachio's confession. In the film, Claudio cries out in agony, "Sweet Hero!"; however, in Shakespeare's script Claudio continues to say, "[N]ow thy image doth appear in the rare semblance that I loved it first" (V.i.239-240). While the original Shakespearean lines help to portray Claudio's sincere repentance, the film script portrays Claudio's intense agony, making the audience love Claudio more than readers of the play generally do. Therefore, the director's choice to remove lines successfully added more drama and emotion.
The film also portrays some differences in characterization. Some are beneficial, some are a bit odd. One beneficial use of characterization is that in the first scene the director decided to make it very obvious that Hero has had a crush on Claudio for a long time and that Beatrice has been in love with Benedick but has also been hurt somehow. We see this when the cousins exchange telling looks at the first mention of Claudio's name in the opening scene. Also, Beatrice portrays a great deal of hurt when she says to Benedick, "You always end with a jade's trick," which is an accusation that he always unfairly drops out of their battles of wits. But more importantly, she shows a great deal of hurt and passion when she lingers on the next line, "I know you of old," clearly telling the audience that Beatrice and Benedick had a romantic past and Beatrice was hurt somehow.
One odd use of characterization is the director's choice to portray Dogberry as a very disgusting person and a drunkard. If we can believe Dogberry's lines addressed to Borachio, Dogberry is actually wealthy enough to own a house, own "two gowns," and is very handsome (IV.ii.74-78). Also, the director chose to take out a lot of Dogberry's lines in which he mixes up words. The only lines of that kind that the director seems to have left in the script are the lines in which Dogberry confuses the word "tedious" for wealthy and says that he would "bestow" all of his "tediousness" on Governor Leonato (III.v.17-21). Sadly, these characterization choices for Dogberry do not help the audience to see Dogberry's importance in revealing the city's leaders to be the fools that they are.