"Each camp will celebrate its champion and deride the adversary," the daily Le Parisien newspaper said.
The influential daily Le Monde said the debate was unlikely to turn the campaign round and said the "disappointing" exchange gave little sense of the way forward for France.
The directors of Royal's campaign team issued a statement, denouncing the Opinionway poll, the first issued on the debate, and asked "Who profits from a survey like this?"
Undecided voters
Both candidates are chasing the support of the seven million people who voted for Francois Bayrou, a centrist candidate who was knocked out in the first round of the presidential elections.
Sarkozy, who has led in more than 100 opinion polls since the start of the year, said he did not believe the debate would change the pattern of the campaign.
"I don't think everything is decided by a debate, however much of a media event it may be," he told RTL radio.
An opinion poll published late on Wednesday before the debate put Sarkozy's support at 53.5 percent against 46.5 for Royal, with 86 percent saying they will not change their minds before the May 6 vote.
Royal denied the race was as good as over.
"Opinion polls don't decide elections," she told France Inter radio.
The last - and final - round of the French elections takes place on Sunday.