"Right from the opening tip, you can see Cooper came focused, unafraid, loaded with quality, relevant research," Mediaite's Joe Concha writes. "He asserted himself as the strongest figure of the presentation, candidates included."
Cooper told the Huffington Post he did his homework, studying stacks of research on each candidate leading up to the event, and he proved it on Tuesday.
His first question set a no-bullshit tone, asking front-runner Hillary Clinton if she'll "say anything" to get elected. "You were against same-sex marriage. Now you're for it," he said. "You defended President Obama's immigration policies. Now you say they're too harsh."
Cooper forced the five candidates to confront tough issues throughout the debate, including #BlackLivesMatter and Planned Parenthood, as well as their stances on gun control.
He also received praise for facing candidate electability head-on. "He struck right at the heart of what worries the politically engaged Democrat nervous about Decision 2016: electability, both in the primary and in the general," Salon's Sonia Saraiya writes.
When candidates tried to beat around the bush on those issues, Cooper called them out on it. When Vermont Sen. Bernie Sanders discussed flaws with the no-fly zone in Syria in response to "Under what circumstances would a President Sanders actually use force?" Cooper interrupted him: "But Sen. Sanders, you didn't answer the question."
"Cooper asked pointed questions and forced candidates to address the issues at hand, rather than allowing them to drift off-topic," CNNMoney's Dylan Byers writes.
"The questions were natural in their delivery, difficult in their content and stated with conviction," Concha writes. "And the job is much harder than it looks."
GOP candidate Donald Trump, who live-tweeted what he said would be an otherwise "boring" debate, even gave it up for Cooper:
Other sung Cooper's praises on Twitter as well: