There's a problem with trying to play Much Ado About Nothing in modern dress; these just aren't quite modern people in a modern world. They can seem that way for long stretches, but then - Beatrice snaps, spits, or whispers "Kill Claudio", and it all goes a little strange. The standard solution, by my casual observation, seems to be to set it no later than the Edwardian period - the last time that the combination of an honour culture and assumed aristocratic privilege makes this sort of thing, along with warfare as an extension of family squabbles, reasonably plausible.
Joss Whedon's cheerfully hastily assembled black-and-white movie treatment tackles such problems largely by ignoring them, bulling straight through the script as a reading by some people who happen to be highly competent actors in modern dress. Where modern equivalences can be found for details in the story, they're used; where they can't, never mind. There are occasional oddities; Beatrice and Benedick get a modern-style sexual history, whereas Hero and Claudio preserve their proper sense and assumptions of virginal purity - but even that can be seen as setting up a contrast between the worldly (and mutually suited) lead couple and the more idealistic (and flawed) secondary pairing.
However, there are hints of a darker modernity. These people in smart suits and big limos, fighting killing wars with their own family? The local cops, a bunch of bumbling dolts totally under the thumbs of the patronising rich folk? The reverence for Catholicism, in the person of a smoothly obliging priest? The improvised cable tie handcuffs and polished personal handguns? You know, it's just possible that these characters are actually a bunch of Mafiosi. They're terribly polite about it, of course - they wouldn't dream of talking business in front of the womenfolk (apart from Conrade, who's been sex-changed into a cold-eyed moll and honorary guy) - but the story ends up with a chilly edge if you look at it this way. The problem isn't that anyone contemplates killing anyone else, it's that they do so when everyone was supposed to be kicking back and taking a break from business.
(Like Whedon was, actually...)
But that's just a possibility; Whedon hasn't touched Shakespeare's words, so we just have to fit our assumptions to what ends up on the screen. And it's not like the analogy doesn't work quite well with Elizabethan aristocrats.
Amy Acker gives great Beatrice, by the way - more unhappy and betrayed than aggressive or dangerous, but well able to handle slapstick, love scenes, vengefulness, and Shakespearean prose. She's already got a decent TV career, but one suspects that a few big-movie casting directors will be calling her agent after this one.