Even environmental campaigners say London 2012 will surpass all others in the modern era, with Sydney in 2000 the only serious runner-up and the smog-clogged Beijing Olympics in 2008 lagging behind.
Friends of the Earth senior campaigner Jane Thomas told AFP: "There's been some huge principles that have been good -- about no private vehicles arriving, recycling, the water supply, the principle of reusing the facilities.
"That's already set a benchmark for things that come in the future, and that can only be applauded."
When the Games start on July 27, spectators will take public transport -- thanks to a deliberate lack of parking spaces -- to an east London Olympic park studded with recycling bins aimed at a tough zero waste to landfill target.
The former industrial site has been cleaned up, with two million tonnes of contaminated soil washed in an on-site soil hospital, to become a wetland park planted with 300,000 plants and 2,000 native trees.
Millions of meals of sustainably-sourced fish and local meat in compostable containers will be bought at a giant, entirely recyclable McDonald's, whose cooking oil will become biodiesel to power its trucks.
And fans will watch cycling greats in a showpiece energy-efficient, naturally ventilated arena, half the weight of the Beijing velodrome.
"We've put a marker in the sand for managing sustainable events," David Stubbs, head of sustainability for London 2012, told AFP.
Sydney's Games left a legacy of solar panels and a big urban renewal project, but Stubbs said London had gone much further.
Beijing installed large areas of solar panels but sustainability standards were patchy in other areas, while many of that Games' lavish purpose-built venues are now crumbling.
"The Green Games programme in Sydney was brilliant but Athens and Beijing didn't really follow up," said Shaun McCarthy, head of the Commission for a Sustainable London 2012, a watchdog for the Games.
London has, however, made its own concessions to practicality.
These have included axing an on-site wind turbine, halving renewable energy use from a planned 20 per cent, and lighting the Olympic flame with ordinary propane and butane.
The sustainability commission criticised other decisions including heavy steel use in the pointless Arcelor Mittal Orbit, a 114.5-metre tall, 1,500-tonne tower.
It also lamented the production of tonnes of merchandise from polluting plastics with no guarantee of an ethical supply chain.
Games sponsorship has meanwhile become so contentious that campaigners set up an ironic award, Greenwash Gold, for the sponsor covering up the worst environmental offences.
The main stadium's wrap advertises Dow Chemical, which owns the firm behind the 1984 Bhopal disaster, while metal for the prized Olympic medals comes from a Utah mine where owners Rio Tinto face a pollution lawsuit.
"Dow, with the Union Carbide factory, is particularly problematic... they could have done an awful lot more to have progressed that satisfactorily and taken on the moral responsibility," said Friends of the Earth's Thomas.
Some London green activists have meanwhile wrangled with whether to support a one-off event requiring huge construction work and mass air travel.
Jenny Jones, Green Party member of the London Assembly, said: "If we wanted to keep hosting these extravagant Games every four years, the greenest option would be to tour around four or five cities that already have everything in place."
Campaigners say the Games' green credentials can only really be assessed afterwards.
Keen to avoid white elephant venues, organisers want the site to stay in use and regenerate a deprived area.
But the main stadium has yet to find a long-term occupant, and in an unpromising sign, Andy Altman, head of the London Legacy Development Corporation, recently announced he would resign in August.
Sponsor Coca-Cola has however developed a permanent new recycling plant in Lincolnshire in the east, while McDonald's says it will make lasting changes to its British supply chain.
McCarthy said the International Olympic Committee should demand far more such commitments.
"The sponsors are keen to get involved -- they're not dragging them there kicking and screaming," he said.
Thomas said the very prominence of the green debate was a sign of progress.
"It's the first time anyone's tried to judge it through a green prism, and that tells us we're moving in the right direction," she said.