The answer is
complicated: he's a man who came to the U.S. 30 years ago with $300 in his pocket. He's a former Johns Hopkins adminstrator and scientist with a history of running programs well.
He's a leading radiological scientist whose profile in basic science was not his calling card, but who developed a number of key technologies and even started businesses. And he is the lightning-rod at the center of science and government in his role as director of the National Institutes of health, presenting proposed ethics rules that have angered many in the NIH including, notably, Zeke Emanuel, head of its ethics program.
In this Baltimore Sun piece, the profile of Zerhouni is interesting - pointing to his ambivalence about the ethics rules, his skillfulness in managing both sides of the stem cell controversies, and his bearing as NIH head - what he's like in the office, and what he doesn't do as director.