The question was posed by a friend of mine who'd just finished The Bourne Ultimatum and was surprised how a threequel could be just as good (if not better) than the first two. If you think about it, it's a rare feat: To film a movie not knowing if its success would warrant a sequel, then regroup a production, carve out a new story, and deal with comparison--then do it again?

Typically, this results in at least one dog:
Godfather? Godfather III. Ocean's? Ocean's Twelve. The Matrix? Uh, everything after the first one. Aliens? Alien3. Superman? Superman III. Indiana Jones? Temple of Doom (this is debatable). Rush Hour? Rush Hour 3. El Mariachi? Not if you count Once upon a Time in Mexico. Shrek? erm.....

Here are the few who appear to qualify: (We are disqualifying Lord of the Rings, as all three films were made simultaneously and gives it an unfair advantage. But yes, they were all good.)

Star Wars Trilogy (Episodes IV-VI): There are the Ewok haters, yes, but you can't say Return of the Jedi was soooo far behind the other two that it wrecked the series. (Or maybe you can; discuss!)

The Bourne trilogy: There isn't a weak link. OK, maybe Julia Stiles, but we mean as far as the movie goes.

Three Colors Trilogy (Blue / White / Red): Krzysztof Kieslowski's French-language films were planned in advance but filmed separately, with fleeting crossover between the film's characters. White is the lightest of the other two, but that doesn't make it the worst. OK, there is no worst (though my favorite is Blue).

The Infernal Affairs Trilogy: The Hong Kong film that was remade into The Departed actually came with two follow-ups; one a prequel and the third a sequel. The third one, as in many cases, is not up to caliber of the first two. Still, not the stinker other trilogies have suffered.

 The Man with No Name Trilogy (A Fistful of Dollars, For A Few Dollars More, The Good, the Bad, and the Ugly) Because a lotta Clint is always better than just one Clint.

Samurai Trilogy - Toshiro Mifune as a samurai. Though not quite on the level as a whole to the Kurosawa movies, each film creates an elegant act for the epic novel on which it's based.

Up for debate:
Terminator
Blade
Back to the Future
Spider-Man
X-Men
Rocky

Any others? Do you agree or disagree with what's on the list?  -- Ellen