World leaders have signed a deal on reforming the UN, though critics say it is much weaker than first envisaged.
The summit coincided with the UN's 60th anniversary
UN Secretary General Kofi Annan hailed a protocol obliging intervention in cases of genocide, and reaffirmation of goals to tackle poverty.
But others said progress at the three-day summit in New York fell short of the reforms that were necessary.
Canada, Venezuela and Indonesia were among the critics, while Cuba called the summit "an unforgivable sham".
The meeting, which wrapped up on Friday, marked the United Nations' 60th anniversary and was the largest-ever gathering of world leaders, bringing together more than 150 heads of state and government.
It was touted as an opportunity to reshape the world body for the challenges of the 21st Century.
The 35-page final document establishes a new Peacebuilding Commission to help countries make the transition from war to peace, and agrees there is an international responsibility to protect people from genocide, war crimes and ethnic cleansing.
It sets up a new Human Rights Council, and condemns terrorism "in all its forms and manifestations, committed by whomever, wherever and for whatever purposes" - though the summit failed to settle on a definition of terrorism.
Correspondents say disagreements have meant some of the anticipated advances have been dropped or watered down.
No international definition of terrorism
Plans to reform Human Rights Commission deferred to General Assembly
Commitment to break down trade barriers weakened
Creation of peace-building commission to help nations emerging from war agreed
Obligation to intervene when civilians face genocide and war crimes agreed
Development section backing Millennium goals to tackle world poverty
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There was no agreement on a strategy to prevent the spread of nuclear weapons - a failure Mr Annan called a "real disgrace".
South African President Thabo Mbeki criticised "rich and powerful nations" for allegedly blocking attempts to widen the Security Council to include more developing nations.
Canadian Prime Minister Paul Martin signalled "profound disappointment" that the Human Rights Council was not more powerful.
Australian Prime Minister John Howard recognised that terrorism was widely discussed and was "a grim but inescapable fact", but he said the UN had failed to meet the threat.
However, one of the UN's most vocal critics, US ambassador John Bolton praised the document as "an important step in a long process of UN reform".
"We cannot allow the reform effort to be derailed or run out of steam," he added.
Many of the issues that were ignored at the summit will be brought up at the annual UN General Assembly, which begins on Saturday, when a speech by Iran's new President, Mahmoud Ahmadinejad, will be closely watched for a statement on his country's nuclear policy.