Under no circumstances is Ji-woon Kim's The Good, the Bad, the Weird a great movie, but I found myself genuinely impressed with it. The pitch – "Korean comic spaghetti western" – sounded like the sort of ultra-hip, insubstantial, self-consciously campy Asian actioner I've grown tired of; I kept flashing back to Riyuhei Kitamura's much-hyped but totally useless Versus, an acquired taste I haven't acquired. I needn't have worried. Though Kim's western pastiche may be insubstantial, it's anything but a drag. It's masterfully directed, legitimately funny, and legitimately fun, thoroughly enjoyable even at an excessive 129 minutes.

Though you may think you're here to see how Kim (whom you may remember from his terrific horror entry A Tale of Two Sisters) plays with the western genre, you're really here for the action sequences. There are two spectacular ones: the rollicking train robbery that opens the film, and a later all-stops-out chase scene involving several gangs of bandits and the Japanese army. These aren't the sort of scenes that bring you to the edge of your seat, but rather the sort that put a steady, delighted grin on your face. Unapologetically goofy, absurdly attenuated, brilliantly paced, and backed by a rousing musical score, they alone make the film worth sitting through.

The Good, the Bad, the Weird is less remarkable as a western than as an action film. The title refers to three Manchurian gunslingers, all after the same mysterious treasure map: "the Weird" (Kang-ho Song) is a scrappy, klutzy thief and crook who accidentally comes across the map during the aforementioned train robbery; "the Bad" is a ruthless but insecure bandit (Byung-hun Lee); "the Good" is a bounty hunter and sharpshooter (Woo-sung Jung). Unsure of each other's motivations, the Good and the Weird team up to secure the map and reach the treasure site lest either the Bad or the imperialist Japanese beat them there.

At first glance, the plot seems to have the genre's hallmark simplicity: the main story hook is a classic McGuffin, something that everyone wants and is willing to kill for. But as the film struggles to fill its over-two-hour running time, it becomes more and more stupidly convoluted, adding an unnecessary subplot and culminating in a flashback revelation that's bizarre and confusing – the only time the film begins to resemble the too-cool-for-the-room Asian action flicks I alluded to earlier.

There are some western touches beyond the story – desert setting, horses, the occasional quick-draw contest – but they don't contribute much. The "western" classification is basically irrelevant. Or, better: it has little to do with why The Good, the Bad, the Weird works. Train robberies may be a western staple, for example, but the disorienting, purposely garish way Kim stages the one here doesn't really resemble any conventions of the genre. Ditto for the main characters, who – with the possible exception of "the Good" – are flamboyant in ways that real western heroes and villains would consider unseemly.

What's left is Kim's prodigious ability to stage preposterously entertaining action scenes, which themselves freewheel past any genre boundaries. These are so good – and so self-contained – that it hardly matters how they fit with the rest of the film. Two days after seeing it, I don't recall many of the plot specifics, but I damn well remember the wonderful, completely ridiculous jeep-horse chase sequence, which goes on longer than you'd think would be wise, but ends up better for it. There's another scene involving a diving helmet that I'll probably remember years from now.

For all that I've berated the film's substance, I should note that the ending features a twist that's nifty and even unpredictable. And if by the time we get there we're a little weary, well – what do you expect from a two-hour Korean spaghetti western?

I for one expected much less than this.