David Walsh, author of the Lance Armstrong book, "Seven Deadly Sins," tweeted, "First reaction is Oprah began the interview brilliantly with her series of 'yes or no' questions. It felt good to hear him admit to doping."
The reaction included Brennan's USA Today column headlined, "If Possible, Armstrong Less Likeable After Oprah."
"He was even more unlikable than one might have imagined. He was smug. He was curt. He was cold and unfeeling," Brennan wrote.
But more legal troubles could be on the horizon for the former Tour de France winner after this tell-all interview.
"He's opening himself up to an enormous amount of possible civil litigation here that could lose him millions of dollars," ABC News legal analyst Dan Abrams said.
Additional reporting contributed by Alexis Shaw, Katie Kindelan, and Colleen Curry.