I've really enjoyed director Freddie Francis' work with Hammer Films over the years, and it was intriguing to see him attached to a lower-budget project and see how he'd do, with lesser-quality actors and production values. It's not bad, just lagging in places, and seems a tad too close to Stephen King's 'The Tommyknockers' later on, for comfort (though that could be due to the novel it's from 'The Gods Hate Kansas' rather than the film).
The apparently high degree of sexual attraction the two hot ladies in the film have for the protagonist, Dr. Curtis Temple, is hard to believe--unless they simply went for his bankroll or had 'daddy' issues. Although Robert Hutton, who plays him, was only 47 at the time of filming, and the actresses who portrayed his assistant Lee Mason and the girl attendant at the gas station were 36 and of unknown age respectively, he looks at least 55 and that he could be the Mason's father and perhaps the attendant's grandfather. Bad casting in that regard, although they're more than capable for the modest complexity of their parts.
I liked the fact that unlike most other science fiction films, the potential of working together with the invasion force as a possible alternative to the tired, seemingly inevitable probability of war with the invading force was explored. Science fiction and horror are extremely popular filmmaking genres that have stood the test of time because they offer us clever avenues as metaphors for examining closely issues that affect society today. The time has certainly come in which people have to stop and intelligently discuss topics that concern us, rather than cling doggedly to our dogma, and to Hell with anyone that dares think any differently than we do. Frankly I feel that it's the only hope that we as a civilization have.