It's been a full decade since the last Men in Black sequel, which is why it was so worrisome to hear, during the production of Men in Black III, that they were working without a finished screenplay. I mean, they had ten years to write it, for goodness' sake. That uncertainty translates to the screen--particularly in the opening scenes, which are all but drenched with flop sweat. It's particularly dispiriting coming from a franchise whose inaugural chapter worked precisely because it had a good script that made it smarter and sharper than the average summer blockbuster; Men in Black was, yes, a giant hit thanks to Will Smith's charisma, his chemistry with Tommy Lee Jones, and Barry Sonnenfeld's jazzy direction, but it was also blessed with a genuinely witty screenplay by Bill & Ted writer Ed Solomon. That component was sorely missing in the inferior Men in Black II, which was not a terrible film but certainly wasn't a good one either. That summary pretty much holds for chapter three.

The picture opens with the daring escape, from a lunar super-max prison, of Boris the Animal (Jemaine Clement, from Flight of the Conchords), a "Boglodite assassin" put away back in 1969 by Agent K (Jones). That sequence includes a "you complete me" joke, which would've been stale by the time the first MIB movie hit screens in summer of 1997, but on we go: the premise is that Boris gets his claws on a time-jumping device that enables him to go back to 1969 and kill K before his arrest, resulting in a time ripple where present-day Agent J (Smith) remembers K but no one else does, since he's been dead for 40 years. To save his friend, J time-jumps back to 1969 as well, where he meets up with the younger K (Josh Brolin) and engages in some groovy '60s comedy.

The mechanics and logistics of the twisty plot are engaging, particularly when it comes to Griffin (the ever-valuable Michael Stuhlbarg), a savant who can not only see into the future, but can see all of the different possible versions and variations of it. The time-jumping sequences themselves are, simply put, awfully cool (and the first is preceded by a sequence atop the Chrysler building that confirms, in the shadow of Mission: Impossible--Ghost Protocol and The Grey, that today's filmmakers are simply trying to trying to kill all of us vertigo sufferers), and the circa-1969 New York production design is impressive. The 3D is, much to my surprise, actually enjoyable; it's a good match for Sonnenfeld's whizzy pop style. And for that matter, the fish-out-of-water stuff isn't nearly as broad or obvious as you might fear, since the filmmakers seem to realize--correctly--that Austin Powers has pretty much done that material to death. And I like the film's theory about Warhol.

But in the grand scheme of things, those are minor pleasures. The film's primary asset--the only pressing reason to see it, really--is Josh Brolin. Though he and Jones shared no scenes in No Country for Old Men or In the Valley of Elah, he has the older actor down cold: not just his cadences and demeanor, but his bone-dry comic timing. Frankly, he does all of the movie's heavy lifting, both comic and dramatic--Smith is pretty much doing his same old schtick (and it's starting to wear thin), while Jones is little more than a glorified cameo. With a brilliant impersonation that is also a fine performance in its own right, Brolin very nearly saves the picture, single-handedly.

But it's not enough. Watching Men in Black III, I was reminded of another sequel to a summer blockbuster: Back to the Future Part II, which was so busy tying itself up into ingenious time-travel knots that it forgot to put in any jokes. MIB3's screenplay shenanigans take a toll; the script is solely credited to Tropic Thunder co-writer Etan Coen, but Smith's Fresh Prince of Bel Air writer Michael Soccio and exec-producer Steven Spielberg's go-to guys David Koepp and Jeff Nathanson all took whacks at it, resulting in a bouillabaisse sorely lacking in a singular comic voice. The premise is clever, Brolin is aces, and there's some lovely pathos at the end. It's a shame it's not funnier.

Jason lives in New York. He holds an MA in Cultural Reporting and Criticism from NYU.