The story is one that is very fanciful and enjoyable. Two incongruous friends, Tommy and Jeff (Gene Kelly and Van Johnson) are hunting in Scotland when they come upon a town not on any map. Brigadoon is a lovely village but it soon becomes obvious it's a town out of time. Actually, it's a magical town that is stuck in the 18th century and it appears and then disappears every 100 years--which is a serious problem as Tommy has fallen in love with one of the residents (Cyd Charisse).
I liked this film quite a bit, though it did have two flaws. The sound stage was too often an obvious sound stage--with obviously painted mountains as a backdrop. Also, I think it might have benefited if they'd made Jeff less of a completely cynical jerk. It was odd seeing a nice-guy actor like Van Johnson playing a nasty little alcoholic and they part could have been better without the crabby aspects of the character. However, the music is lovely, the story sweet and there is still a lot to admire in this film.
I happened to watch the 1966 made for TV version of "Brigadoon" a week ago--and I enjoyed it enough that I sought out the original theatrical version from 1954. Both, naturally, are very similar though there are a few differences. First, because Gene Kelly and Cyd Charisse were in this Hollywood production, naturally there would be more dancing than singing. Second, oddly, the story of how Brigadoon came to be was changed for the 1954 version. I have no idea why. And, finally, the 1954 version was made to look like a typical Hollywood production that was, as I mentioned above, made in a sound stage--and the 1966 version had a few actual outdoor scenes and much of the rest looked like it was on a theater stage. Both are very watchable, though I prefer the 1954 film. If you would like to see the 1966 version (starring Robert Goulet), it is available to watch free at archive.org.