While it's true that "Phase IV" is rather slow moving in spots, and that the human characters are ciphers with no real depth to speak of, "Phase IV" is a nice sally at an experimental science fiction film that emphasizes mood and dread over action and character development.
I had the good fortune to watch this on a really large flat screen TV, and the amazing insect photography (major kudos to the editor who managed to integrate it so completely into the story!) and dissonant synthesizer laden sound track come through nicely with good viewing equipment - they add the proper utterly alien and inhuman feel to the movie and turn something pretty good into something really creep and spooky.
Although the characters are admittedly pretty flat, that's undoubtedly on purpose. "Phase IV" is all about the subjection of the human characters to the overwhelming power of a hive mind where "personality" is besides the point. Even so, Nigel Davenport brings the good stuff to his role as the biologist trying to contain the ants, and you both know everything you need to know and everything you'll ever know about in the first five minutes...without ever knowing him at all.
An ambiguous and otherworldly/mystical ending might not sit well with a lot of viewers who like their science fiction movies to wrap things up by the end. And, OK, the goofy little montage at the end with the mathematician and the gamin doesn't really match the quality of the hallucinatory insect footage that preceded it.
Still, Saul Bass knew how to present an otherworldly, truly alien experience, but he was probably just too far ahead of his time.
A classic of sorts.
