Usually spliced together by a team of publicists, the most effective previews show the audience exactly what they want to see—with the promise there's more where that came from. The best previews do that, too, but they don't have to lie in order to do it.
Take the trailer for Quentin Tarantino's Inglourious Basterds, which promises a Dirty Dozen-style action flick about a crew of Nazi-killin' Jews in WWII. It's a sharp trailer, witty and dark and visceral, and it makes you want to get to the theater ASAP.
It's not that Inglourious Basterds' trailer is an all-out lie—there is a group of Jews called the Basterds, and they do kill some Nazis. Brad Pitt plays their leader, and whenever the Basterds are onscreen, Tarantino's latest feels exactly as one would hope: as if Tarantino lifted samples from every kickass WWII flick, from The Guns of Navarone to The Big Red One, then remixed 'em into something wholly new and exhilarating.
But here's the thing the trailer doesn't tell you, and which I feel obligated to point out: the Basterds? They aren't in Inglourious Basterds nearly as much as you'll want them to be.
Which isn't to say that the rest of Basterds is lousy, 'cause it's not—overall, this is a hell of a picture, and parts of it are as great, if not better, than anything else Tarantino's done. Basterds' opening sequence is a nerve-wracking exercise in tension: throughout, there's a dark humor that'll make you snicker and clench your teeth; there are killer performances from Pitt and Christoph Waltz, who plays a particularly vicious Nazi named Colonel Hans Landa, AKA "The Jew Hunter." (Pitt's character, a charming, totally fucked-up Tennessean lieutenant named Aldo "The Apache" Raine, demands his soldiers scalp the Nazis they kill and gleefully carves swastikas into the foreheads of those he lets live; Landa, meanwhile, is so terrifyingly fascinating that he'll go down as one of the best movie villains in recent memory.)
And then there's the rest of Basterds, which is a sizeable chunk, and which never works as well as the stuff above: Shosanna Dreyfus (Mélanie Laurent) is a Jew hiding out in Paris; Fredrick Zoller (Daniel Brühl) is an eager-to-please Nazi war hero; Bridget von Hammersmark (Diane Kruger) is a German movie star who's secretly working with the Allies. All of these characters' plots are woven into a grandiose opera, but if there's a consistent tone to be found in this film as a whole, Tarantino doesn't seem interested in finding it. While the best parts of Basterds channel the splattery pulp of old comic books, the worst sequences can feel indulgent and melodramatic.
Don't misunderstand: Tarantino's still really fucking good at what he does. It's just that judging by Inglourious Basterds' trailer—which might not be fair or smart, but which, regardless, is something most people will do—one sees a version of this film that's Tarantino at the top of his game, with Pitt slyly drawling out razor-sharp dialogue and WWII looking and sounding like it never has before. Inglourious Bastards is totally like that sometimes, but not all the time—which is kinda disappointing, but is mostly just a good reminder that previews lie.