War In Space was released in 1977 and intended to be a direct sequel to Battle In Outer Space (1959). Unfortunately for its creators, I found it to be more similar to Atragon (1963) than Battle In Outer Space. Unfortunately, I was not that pleased.
Let's start with the plot because plot is perhaps the most important thing about a movie (in my opinion, at least). The story is dry and leads to an uninteresting script that gives the actors little to work with. Everything is black and white; the intentions of the characters are spelled out in the first few minutes of the movie. Unfortunately, nothing is really left to the imagination. I'll cite the love subplot as an example. Guy A and Guy B both want Girl; Girl wants Guy A. Guy A and Guy B are good friends, so Guy A leaves Japan so that Guy B can get Girl. When Guy A returns, Guy B and Girl are engaged. When Guy B dies at the hands of the enemy, Girl barely sheds a tear; I'm not sure if this is due to bad acting or a bad screenplay (or maybe some of both), but I don't get the idea that Girl was ever really interested in Guy B. She has no problem rushing into the open arms of Guy A once Guy B is killed. At least she cries a bit more when her father dies. The film itself is fairly emotionless. Beyond a feeling of "we need to kill the bad guys," no character depth is ever established. I was sick of the characters very quickly. In Atragon, former Japanese Navy officer, Jinguji, goes through several emotional dilemmas, as does his estranged daughter; although the love story between the daughter and a reporter is always only implied rather than stated, it almost works better this way by not distracting from the importance of the tenuous father-daughter relationship.
Next, let's talk about the music. War In Space's music is some of the most uninspired movie music I've heard since Godzilla vs. Megalon (1973). The composer takes the concept of Akira Ifukube's war march (a couple of which feature prominently in Atragon) and stomps all over it, creating something that I dare to call a mockery of the genre. The inclusion of the wahwah guitar in the march make the scenes in which it figures almost hilarious (unintentionally, I'm sure); I would expect to find these sorts of things in Gamera films, aimed at children. Atragon's music is expertly crafted to bring out a breadth of emotion: Jinguji's theme is constantly torn between stately and sorrowful, and the modal scale of the Mu theme provides an air of exoticism.
The picture quality looks the same in both Atragon and War In Space. Given that Atragon is 14 years older than War In Space, I would have expected some improvements to have been made, but there seem to be none. Perhaps this is really a testament to the Atragon team (Tanaka/Honda/Tsuburaya/Ifukube) that is so often credited for the successes of Toho's 1950s and early 1960s tokusatsu films. The redeeming quality of War In Space is that its earth-destruction scenes look fairly good; Teruyoshi Nakano seems to have vastly improved since the days of Godzilla vs. Gigan.
Since I've said nothing bad about Atragon so far (biased, much?), I'll say one thing that has always puzzled me about the film. If the Mu Empire were so powerful and advanced, why didn't they "reclaim" the surface of the earth before the humans became more advanced. It's much more easy to destroy huts made from clay with your laser beam in the shape of your underwater dragon deity than it is to destroy concrete buildings. Morever, I think the humans of several centuries past would have easily surrendered and would have viewed the people of Mu as gods. But, oh well. There'd be no plot if this were the case.
In short, I feel that War In Space reflects a general decline in the quality of Toho's kaiju/tokusatsu films in the 1970s. I am unaware of the forces which contributed to this downfall, but I can say with much certainty that War In Space fits in with some of its 1970s counterparts (especially that wahwah surf guitar).