I think this was Toho's fourth "giant monster on the loose" movie, and it's also probably the least known. The American "version", "Varan the Unbelievable", is a travesty and should be avoided at all costs.
The Japanese original has some really good things about it. It features one of Akira Ifukube's best monster-movie scores, in which he introduced some themes that would be re-used in practically every kaiju eiga that followed... There's also a wonderful "Lovecraft-gone-Japanese" feeling about the protagonists' arrival in the village: they interrupt a strange ceremony, and a sea of masked faces turns to watch them. This is followed by an eerie scene as they follow a mist-shrouded path to the forbidden lake.
Unfortunately, the rest of the movie is a little uninspired. It doesn't have the emotional tension of "Godzilla" or "Rodan", although the monster costume and attack scenes are very, very good.
