Peter Jackson recently announced that his upcoming adaptation of JRR Tolkien’s The Hobbit will be released as a trilogy, not in two parts as originally planned. Whether this is necessary artistically, or whether it is a move by the studios to milk more money out of the franchise, remains to be seen.

The news followed hot on the heels of the release of the third and final instalment of Christopher Nolan’s Batman trilogy, The Dark Knight Rises, arguably one of the greatest trilogies ever released. It offered a rare thing in movie trilogies; consistency. Which brings to mind the question: what makes a great movie trilogy, and that considered, what are the greatest trilogies that have ever been released, and which ones don’t cut it?

Defining what makes a great trilogy is open to debate, but for the purpose of this exercise, in order for a trilogy to be great it must contain three great films. Any weak links, whatever the standard of the other films, and it fails to reach the necessary criteria. The Matrix trilogy, the first film of which is a stunning, mind-blowing, ground-breaking piece of cinema that changed action-movie lore forever, is not a great trilogy because its sequels, although not terrible, are not particularly great either. When Brett Ratner took over the helm of X-Men from Bryan Singer, his loveless approach to directing ensured that the series could never be considered great. Sam Raimi’s overly-ambitious Spider-Man 3 failed to reach the heights of his first two films, making certain that all three could not be granted a place among the movie-trilogy elite. And then there’s The Godfather trilogy. Thanks Sofia Coppola.

Then you have the threesomes that simply shouldn’t exist. In bringing a second Star Wars trilogy to our cinema screens George Lucas showed himself to be sadly misguided. In recent years, he seems to be intent on undoing the good work of his original trilogy, replacing its magic with CGI and effects and Hayden Cristensen. The Mighty Ducks trilogy’s existence goes a step further, defying any real logic. The first film is bad and it only gets worse from there. And the El Mariachi trilogy ends on such a bum note with Once upon a Time in Mexico that it more than cancels out any of the good work of the first two films.

And so we move on the three-pieces that can rightly be called great. The ones that have no weakness. Three great films that make a great trilogy. George Lucas may have tried to undo the good work of his original Star Wars trilogy but that original trilogy still exists, and it is still great. The words Return of the Jedi may be popping up into heads at this moment. Go back and watch it. You do not hate the Ewoks as much as you think you do. The Dollars trilogy – A Fistful of Dollars, For a Few Dollars More and The Good, The Bad and The Ugly – is equally flawless, combining Clint Eastwood’s gruff attitude, Sergio Leone’s masterful direction and Ennio Morricone’s gorgeous music to near-perfect effect. Pixar’s Toy Story trilogy never lets up, each film offering just the right dose and the familiar and the new, while Peter Jackson’s Lord of the Rings trilogy is of a consistently high standard all the way through.

And with Peter Jackson we come full circle. A great trilogy is a difficult thing to produce, and with questions always being raised as to whether sequels are being made for the right reasons, art before money, it’s hard to know when we’ll get another one. The Hobbit may prove its worth. We’ll have to wait and see.