I can't believe that some people compare this movie favorably with Beast From 20,000 Fathoms. Behemoth is a near carbon copy rip-off of Beast,shamelessly using many plot elements from the previous movie. Among these are:the creature destroying an isolated structure(A lighthouse for Beast,a farm for Behemoth),picking up a car in its mouth and shaking it before dropping it,knocking a building over on people,causing mass death and illness(a disease for Beast,radiation for Behemoth),that they were both spawned at the mouth of a river,and that both are killed by having a nuclear projectile fired into them.
But the worst flaw in this movie is the terrible stop motion technique. This creature has none of the personality of the Beast,it is simply a mindless juggernaut. The head and body movements are stiff,clumsy and repeated ad nauseum,as is the roar,which never changes tone once. The movie does have a few good points-Gene Evans as the young,brash American,melds well with Andre Morell's quiet,efficient effort. The radiation emitted by the creature is well done,and the resulting corpses are gruesomely believable. However this movie,to me,is one of the worst of the "Giant Lizard stomps Big City" genre.