Given his CV, I’d say yes, he was/is highly regarded by for his contributions to the field of astronomy and space exploration.
Apart from his genuine contributions to science, he is far more famous as a popularizer of science - not just for clearly and effectively describing difficult concepts to non-scientists, but for his gift of passionately explaining the profound implications and significance behind many of the concepts he described.
I did lose some small measure of respect for him when I found out about his legal battle against Apple. I can understand him not wanting them to use his name on one of their computer chips for fear of implying endorsement, but when Apple complied by removing his name and instead calling the chip BHA (for “Butt-Head Astronomer”), I think Sagan should not have pursued legal action.
One thing I wonder about with “how well regarded is he by his peers” is how impartial the peers are. Are they jealous because someone doing similar work hits the jackpot and becomes famous and maybe rich? It’s interesting how some great athletes will speak disparagingly about their successors who make more money (Bob Feller on Nolan Ryan, Wilt Chamberlain on Kareem Abdul-Jabbar).
Kunilou mentions a co worker who took a Sagan taught class. One high school classmate who was smarter and more driven than me (take a summer off to work on an Indian reservation? Not me, I’m going out of nights and to the beach on weekends) got into Harvard. His first semester he took an intro Economics class with John Kenneth Galbraith, who taught it to keep him fresh on economic principles. He described Galbraith as a good teacher but gave the impression that he was drunk at times.