The map in question has been sold by an underworld crime boss who has also employed The Bad to steal it back, thereby securing the cash and said map but, before The Bad can get his hands on it, it is found by The Weird during a train robbery. He becomes convinced that it gives the details of a buried treasure site and heads off the find the "gold".
The Good, while searching for The Bad (to catch him and get the bounty on his head), stumbles across The Weird and, unsure of each other's motivations, they grudgingly agree to help each other by:
a) Catching The Bad, and
b) Finding the treasure before either The Bad or the imperialist Japanese can get to it.
However, unknown to The Weird, The Good also plans to get the bounty on The Weird's head, once he has served his usefulness.

The overall plot essentially deals with the chase between the three to get/keep the map, find the location alluded to on it and find the buried treasure, but is, in truth, simply a ploy to provide some exhilarating sequences and get the three characters to a point where they can battle it all out man to man.

Regardless of the tag lines that have been attached to the movie, or the trailers specifically edited to push the spaghetti western aspects, "The Good, The Bad, The Weird" is actually as much action as spaghetti, as much comedy as western – a film that shamelessly draws on its influences and parodies the hell out of them.
Ok, so it isn't multi-layered; there's no real "good will triumph over evil" Western ethos present; there's no morality tale in play and the outcome isn't going to change your views on life, the universe or anything, but if that's what you're looking for, you're kind of missing the point.
The Good, The Bad, The Weird positively screams exhilaration from every frame and illicits an excitement that has long been missing from most action films.The camera work and the production values are top notch and are used to give a huge sense of movement to proceedings which are already rolling along at a pace.
Add to that, the fact that director Kim Jee-woon has an amazing ability to stage massively entertaining action sequences which are so good that they could almost stand on their own, with or without the remainder of the film, and the overall result is simply thrilling. The main chase sequence, ablaze with guns, horses and jeeps, is a little longer than is healthy, but you'll have such a grin on your face throughout that you'll happily let that fly.

Korean films tend to have copious amounts of incredibly intelligent black humour wrapped up in whatever genre is being played and The Good, The Bad, The Weird is no exception, with most revolving around The Weird and giving Song Kang-ho a chance to show that he is as good at playing comedic roles as he is at drama.
If you need more incentives then believe me when I say that another scene involving a diving helmet will stay with you long after the film ends (and possibly forever) and a beautifully unpredictable little plot twist at the close of the movie rounds the experience off to a tee.

Cast:

The entire cast play their parts with suitable aplomb but extra mention should be made of Kang Song-ho (The Weird) and Lee Byung-hun (The Bad) whose performances are exceptional. Both exude a noticable pleasure in their roles and add a significant depth and a tremendous amount of humour to proceedings. Jung Woo-sung (as The Good) also does everything that is required to create as memorable a character as possible but, lets face it, bad guys are almost always more interesting and memorable than good guys - that's just the way it is.


Summary:

A fun-filled, exhilarating rollercoaster ride with a group of characters who wouldn't be out of place in a mental asylum.