The wartime US experiments were trying to learn the rate in which plutonium was excreted from the human body. It was not an obvious thing (because plutonium is a man-made element with complicated chemistry) and not an easy thing to learn from animal experiments (because animal models are not exactly the same as human ones). Much of this work was done during the Manhattan Project, in the service of being able to set exposure standards for workers — if plutonium left the body very quickly, or very slowly, then one would adjust the amount of time one was exposed to it accordingly.

Did they learn anything? Sure. They learned the excretion rates. The science they were doing was not itself flawed; it was basic toxiological work. The problem is that they did it without informed consent of the patients, both because it was being done under the secrecy of war, where the very existence of plutonium was a secret, much less the fact that the US needed to know exposure standards for it.

Unethical? Definitely. Bad science? No. It wasn't mad scientist stuff like Mengele was doing. It was public health science done inappropriately. One could imagine them doing the same work but getting informed consent from the patients and it being considered fine science indeed.

But because it had been done unethically and secretly, the Atomic Energy Commission (AEC) decided that it was worth keeping secret. Why? Because they feared the bad publicity that would come with its revelation, even though the work had primarily been done by the Army, not the AEC. The AEC was at the time a very weak and new organization, and feared that any scandal would lead its enemies to eliminate it. The result was that they kept the secrecy in place, and even extended it a bit into the Cold War with other unethical experiments done in the name of national security. Again, this would have been totally "fine" science except for the consent problems. (The same cannot be said for all secret US science — it is far less clear that the CIA's MK-ULTRA program, for example, created anything of great value, unless you consider the Grateful Dead a worthwhile spin-off result.)

Most of the writing on the radiation experiments is in a polemical, "can you believe this scandal" mold. There is room for that; it was very unethical. Eileen Welsome's The Plutonium Files (New York, NY: Dial Press, 1999) is of this approach. For a "defense" of the work (or at least its goals and intent, not its non-consensual aspects), see William Moss, and Roger Eckhardt, "The human plutonium injection experiments," Los Alamos Science no. 23 (1995): 177-233.

I don't want to minimize the inappropriateness of the experiments. But at least for the wartime experiments, it isn't clear that actual harm was caused in the small number of people affected, and while the approach to the data was unethical, it was neither unscientific nor pointless. It makes for an interesting ethical question to ask how it ought to have been done, e.g., should they have told the patients and gotten informed consent, at the risk of violating security? Probably. But it's harder to argue they shouldn't have done the human studies at all — the human data was necessary for setting the exposure standards, and those affected thousands of people working in the field of plutonium production.

Some of the later radiation experiments, notably those on prisoners and the developmentally disabled, pose far greater ethical quandries overall, though.