“What did we learn?”

“Not to do it again … I wish I knew what we did.”

These lines come at the very end of “Burn After Reading,” the Coen Brothers’ latest offering, and they are very apt. Here is a movie that spends a very daffy 96 minutes traveling in ludicrous loops and arrives … nowhere. It is the kind of movie that leaves you entertained but empty, one that disintegrates the second it ends and is ultimately a disappointment, especially after the mournful, brilliant “No Country For Old Men.” What is more troubling, there is a moral vacuum at the film’s center, one which leaves us wondering why the Coens even bothered.

It starts on a dizzying high, though. The cast is a moviegoer’s dream: Frances McDormand, George Clooney, Tilda Swinton, John Malkovich and a scene-stealing Brad Pitt all become entangled in each other’s plot points. There are too many knots to loosen here, but the object that sets the ball rolling is a disc that belongs to Osborne Cox (Malkovich), a harried CIA agent. The disc winds up in the hands of Chad Feldheimer (Pitt) and Linda Litzke (McDormand), two workers at a D.C. gym, and they immediately mistake the cryptic numbers (Cox’s finances) and some overheated prose (Cox’s doomed memoirs) on the disk for super-secret CIA intelligence material. Out of this, a blackmail plot is born, with Linda especially desperate to finance all that plastic surgery she’s been longing for. Swinton plays Malkovich’s frosty wife, who’s cheating on him with U.S. Marshal Harry Pfarrer (Clooney).

OK. Got all that? Everyone has his wacko button turned up to 11, and you can tell they’ve all had a ball making this movie. Pitt is especially sublime, playing an endearingly buffoonish, childlike naif. Whether stumbling in his attempts at gravitas during a blackmail phone call or just bopping merrily to his iPod, Pitt is a joy to watch. This is the best performance I’ve ever seen of his, a completely uninhibited and rollicking delight.

While Pitt stands out, the other members of the cast are also very good. Some of them, like McDormand and Malkovich, do that McDormand- and Malkovich-thing we expect and love, and some of them, like Swinton and Clooney, play their broad character types to the hilt. Along the way, we get things like Cold War intrigue, sinister spying, unrequited love and even a very, very unexpected invention that I won’t give away here.

As you can probably tell, “Burn After Reading” is not exactly cinema verité. For much of its running time, it plays as finely tuned satire. The Coens are having fun with a movie that, if pitched slightly differently, could have passed for a standard Washington political potboiler. Many scenes feature pulse-pounding music that almost cries out for a meeting in the war room.

As the plot twists pile higher, you find yourself wondering if there’s any point to all this. The disk is a MacGuffin, something that makes everyone collide with each other but ultimately means nothing.

This makes things enjoyable for quite some time, as the cast is very skilled at collision. But what ultimately drags “Burn After Reading” down is that the whole movie is a MacGuffin.

Nothing winds up going anywhere, and the ending is a complete cop-out, as if the filmmakers just threw up their hands. It becomes clear that there will be no character development or real emotion anywhere on screen.

The most unnecessary element in “Burn After Reading” is its frequent detour into random, senseless violence. While it’s hardly a Coen Brothers movie if at least one person doesn’t have his head blown off, their violence usually has a point to it. “No Country For Old Men” was drenched in blood, but the film had something to say about the evil that produced that blood. In “Burn After Reading,” we get not one, but two brutal murders that serve absolutely no purpose except to jolt us. The casualness with which this violence is treated points to the deep strain of nihilism runnin through this film, one that, in its flippancy, winds up treating its characters with a depressing degree of contempt.

All this makes “Burn After Reading” enjoyable while it is in front of you, but a hard one to really like. The Coens should know better than this. When they make a film that almost begs us not to care about anyone or anything in it, we’re likely to take the bait.