The gathering, which has attracted more than a hundred world leaders, had promised to tackle poverty and damage to the natural world.
But campaigners say few tangible measures have been agreed.
And they have denounced the final text due for leaders’ signatures.
UN Secretary General Ban Ki-moon has urged delegates to seize the moment.
He called on them to match words with actions and show their commitment to sustainable development. He also urged governments to eliminate hunger from the world.
The meeting, marking 20 years since the Earth Summit in the same city and 40 years since the very first global environment gathering in Stockholm, was aimed at stimulating moves towards the “green economy”.
But the declaration, that was concluded by government negotiators on Tuesday and which ministers have not sought to re-open for discussion, puts the green economy as just one possible pathway to sustainable development.
Mary Robinson, former Irish president and UN High Commissioner for Human Rights, said it was not enough.
“This is a ‘once in a generation’ moment when the world needs vision, commitment and, above all, leadership,” she said.
“Sadly, the current document is a failure of leadership.”
The British Deputy Prime Minister, Nick Clegg, went so far as to call it “insipid”.
Former Brazilian President Fernando Cardoso, who chaired the 1992 Earth Summit, said the declaration did not do as much for environmental protection as for human development.
“This old division between environment and development is not the way we are going to solve the problems that we are creating for our grandchildren and great-grandchildren,” he said.
“We have to accept that the solutions to poverty and inequality lie in sustainable growth, not growth at all costs.”
Mr Ban had hoped the summit would take firmer steps towards ensuring the poor had access to water, food and energy.
However, his flagship Sustainable Energy for All initiative was merely “noted” in the text, not enthusiastically endorsed.
The text that leaders will sign at the end of the meeting runs to nearly 50 pages.
Environment groups say it should have contained commitments to phase out fossil fuel subsidies, and to increase the global share of renewable energy. But these pledges are absent.
It does propose setting up sustainable development goals – rather like the Millennium Development Goals, only with a greener tinge – but again, there is no detail and no timetable.
“The overall feeling here is that governments have missed an opportunity to change the course of human development,” says BBC environment correspondent Richard Black.
“But it’s clear not every country wanted a change of tack. The US, Canada and many developing nations appear content to continue with business as usual.”