Basically "It Conquered the World" is the original "Invasion of the Body Snatchers" meets "The Day the Earth Stood Still"  and the quality of those two movies only underscores how pitiful this one looks by comparison. I'll give Roger Corman credit for being the best director who ever regularly worked at American International  not that that's saying much for him  and for at least attempting to work serious political and social commentary into a few of his movies, including this one. Ideologically, "It Conquered the World" is a hard-Right propaganda piece (much the way John Carpenter's 1983 "They Live" took the central premise of "Invasion of the Body Snatchers" and used it for liberal-Left propaganda) in which the Venusian strategy for conquering the world is exactly what the Right of the time said the Communists were doing  targeting political, scientific and military leaders, recruiting them and using them to subvert the country by stealth  and Lee Van Cleef's character is clearly supposed to be what the Right of the time called a "Com-Symp," someone who wasn't an active Communist but so dangerously iconoclastic he was easy prey and all too willing to do their dirty work. But any attempt Corman and his writer, Lou Rusoff, might have been making for serious political commentary is subverted (pardon the pun) by the sheer ludicrousness of the appearance of the Venusian alien. (The makers of the first "Invasion of the Body Snatchers" showed great wisdom in avoiding any shots of the alien invaders in their natural form.) Maybe the upended half-cucumber with toothpick arms isn't quite as risible as the diving-helmeted gorilla who conquered the world in "Robot Monster," but that's damning with faint praise; the ridiculous monster takes what could have been a decent piece of half-serious science fiction and turns it into pure camp.