Part of a litany of late 60s films that recognized the potential power (and fear of things not understood) of the rapidly improving computer systems. Like HAL, Colossus one ups its creators. The use of "B" list actors and borrowing computer equipment that was old at the time doesn't really detract from the story. Watching the general public start to accept the rule of the computers, even to the point of wearing tee shirts similar to those bought at rock concerts with the symbol of the Colossus Programming Office on them, foreshadows stuff that actually is happening today.
Dated, even when it was made, this movie is still good fun.