Fifteen locations are on the shortlist for the proposed 'eco-towns'
Gordon Brown's "eco-towns" policy has suffered a setback after a report said some schemes were not much better than housing estates with green edges added.
The Eco-Towns Challenge Panel said one site at Weston Otmoor in Oxfordshire risked becoming "commuterville".
Another at Curborough, Staffordshire, had an "eco" element which felt like an "add-on", the panel of experts said.
Housing Minister Caroline Flint said some developers "clearly need to up their game."
The panel said the site at New Marston in Bedfordshire "looks like a typical commercial scheme" with no sense of identity.
Opponents of the 15 controversial sites are likely to seize on criticism in the report which is aimed at each scheme's developers.
Ms Flint will decide on which of up to 10 schemes will be given the go-ahead in October.
"This process was meant to be a challenging ride for the developers, and they need to be open to the creativity of these ideas", she said.
"Some clearly need to up their game and the ball is now in their court."
The panel, set up by the government, includes TV presenter Kris Murrin, Wayne Hemingway, the founder of fashion label Red Or Dead, and environmental and transport experts.
Panel chairman John Walker said: "Our brief was to challenge each proposal in a robust and constructive way, and I think we have done a good job on that front.
"We have seen much to admire, but in all cases we are challenging the developers to take major steps forward.
"We want the final eco-towns to be better than the best of the current examples that do exist in the UK and the rest of Europe. Clearly there is still a lot of work to do."
Mr Brown announced last year that he wanted to see five new eco-towns created as part of a general increase in house building to meet demand for homes.
At the 2007 Labour conference, the prime minister said that target would be doubled to 10 eco-towns across the UK.