The aim of all eugenics, by definition, is to improve the "gene pool" — to make population-level effects that would (in the eyes of its proponents) decrease crime, disease, state spending, etc., and instead increase all manner of good things about society. Which is all well and good in the abstract (except for the focus on biology as the real cause of crime, disease, state spending, etc.) until you start talking about what you consider to be a "life not worth living," a condition that you might select for or against, and the means by which you might do it, at which point things tend to get pretty ugly especially in the Nazi period (they killed huge numbers of disabled people, including children, in their "euthanasia" program; they sterilized nearly half a million people against their will in a program that every expert at the time would have known was futile for producing population-level genetic effects; they combined these ideas with racism and anti-Semitism in their repressive laws and eventually genocide; etc.).

The Nazi idea of a "superman" (übermench) is not a superhero of the comics type. When Hitler used the term he just meant something like "superior man" which is to say a person who represented the Nazi ideals of a human being (which is to say, someone who was not a Slav or a Jew or non-white; in the Nazi racial theory defining the opposite, the untermensch, was more motivating than defining the "good" thing). Which is only to say, the Nazi eugenics program was not about producing superheroes or anything exciting like that.

The best coverage of the Nazi theories, methods, and horrors is Robert Proctor, Racial Hygiene: Medicine Under the Nazis (Harvard University Press, 1990).