First: two disclaimers. I saw The Good, The Bad, The Weird in South Korea, and though the theater advertised exclusivity on English Subtitles, the film was all in Korean, of which I only understand about 1 word in 20. The film itself had its own disclaimer stating that the visual effects weren't finished, and the credits were in roman characters, so I think it may have been the cut that was screened at Cannes, or a very similar one.
The film itself was fantastic. The cinematography was amazing, the action frenetic, the comedy, while low brow, was amusing, and sometimes reminiscent of a children's game called "ddong chim." Not being Korean I can't comment on the plot, though the acting seemed genuine enough. The Good "bastard" was good, the Bad "bastard" was bad and the Weird "bastard" was suitably representative of the Korean idea of crazy. I am also not familiar enough with the actors to say whether the performances stand out from their usual work.
The most I can really say about this movie is that I plan to see it again, with English subtitles, to figure out what I missed.