Much better than what the IMDB rating made me expect

For one thing, the scientific rigor of the plot is much higher than the average Hollywood sci-fi movie of today. Yes, there are plotholes, but as a scientist, I must say I was mildly pleased with "Doomsday machine". I liked the plot also because it is unusual, it doesn't follow the Hollywood cookbook. Finally, I thought the acting/directing was OK, especially for a movie from the end of the 60's.