I am glad to see the writers took the job seriously and had the characters ask the questions we asked from the audience. Can the Mysterians be trusted even though they say they are peaceful? Should we ask for a nuclear strike? The Marcolights have a limited range, how can we get around that? Should we wait for the Electronic Cannon or attack right now with the giant airships and Marcolights?
There were a few flaws. For example one of the characters mentioned that a fixed base was a weakness. I assume that is because you can't depend only on a defensive shield. A base must be defended by mobile fighter craft as well. The flying saucers performed that function until they unexpectedly retreated to the base during the climatic battle. The other weak point was the giant airships Alpha-1 and Beta-1. They moved like zeppelins and the standard cannon seemed weak. I guess their plot purpose was to be shot down so that Beta-2 could built for a second attack on the Mysterian base.
If you saw this movie as a kid it is still enjoyable as an adult. If you've never seen it then it is probably only of interest to those who want to see the early days of Japanese monster movies. You may be pleasantly surprised to see the leader of the Seven Samurai as the head scientist.