I freely admit that I wasn't expecting much from Men in Black III. The 1997 original is an okay Ghostbusters (1984) wannabe and nothing more. In 2002, a sequel was thrust upon us and it's a text book example of a soulless, money-grubbing rehash. So, you can imagine my pleasant surprise when turns out to be, by far, the best in the series.
A mad dog killer of an alien named Boris The Animal (Jemaine Clement of "The Flight of the Conchords") escapes his imprisonment and time travels back to Earth of 1969 to murder the man who captured him, Agent K (Tommy Lee Jones). To save his partner, Agent J (Will Smith) travels to 1969 in pursuit.
Josh Brolin plays the young version of K when the film jumps to the past, and he doesn't just do a party trick imitation of Tommy Lee Jones. It's a full fledged performance, so good that it never really registers that Jones isn't in that much of the movie because the bridge between the two actors is seamless. As for Smith, he has matured as an actor over the years and here he keeps the mugging in check to good effect.
The screenplay, credited to Etan Cohen (Idiocracy, Tropic Thunder), is clever, but doesn't over exert its time travel premise, and in terms of direction, this is Barry Sonnenfeld's strongest effort, resulting in a film that is funny, moves at a good clip, and has an emotionally affecting payoff. Seriously.
There's also a side-splitting scene with Bill Hader as Andy Warhol, and if you are thinking that Warhol turns out to be a space alien, you would be wrong. This movie is smarter than that.
Now, K's flirtation with the lovely Agent O (Emma Thompson in the present and Alice Eve in the past) could have been explored a little more, and Boris' voice is kind of annoying. In return, though, we get an extremely cool Rick Baker creature design that is reminiscent of his Nazi werewolves from the horrifying dream sequence in An American Werewolf in London (1981).
I understand that Men in Black III might be a hard sell because the previous one sucks so bad and the original doesn't date all that well, but this film is really terrific entertainment.