It is interesting to note that the previous Brunner novel that I read (Quicksand) and this one were written in the same year. They are very different in some ways, but both are failures. Where Quicksand seemed like an attempt to write a mainstream novel with a slight speculative element, Born Under Mars, seems like a throw away novel written entirely for money. My guess is that Brunner was tossing about trying to find a successful format and resorted to space opera in order to pay the bills.
Born Under Mars is a dark, noir piece without much going on. Usually a Brunner novel has dozens of Science Fiction ideas thrown into a mix where few are explored. This is one of the good things about Brunner. Every book is full of ideas just thrown out and then ignored, any of which could make a whole different novel.
Born Under Mars is very sparse as far as new ideas are concerned. Brunner knocks of a novel about a kidnapped baby that seems to drag. There were very little discussions of motive and a great many coincidences that seemed contrived to fit the loose plot. There is point where the main character has his memory altered and wanders around for a few pages, but there is no real reason why this was done, how it was accomplished, and the reader is surprised that it happened at all. Brunner just keeps writing as though he had no outline or even an idea where the plot is headed.
1967 was not a good year for Brunner. I prefer the earlier pure space opera and the later "big theme" novels. In 1967 Brunner was scratching out the bad novels and not producing anything readable.