The experts - from design, the environment and transport - have published their initial recommendations on the first schemes.
The concerns for the Communities & Local Government-appointed panel include the fact that many of the schemes looked like "typical commercial developments".
General comments from the panel on the proposals include the issue of how developers would ensure high design quality, and that they must show how a strategy for functional green infrastructure - for example, green spaces and corridors - will provide an attractive setting for development.
The panel also wants proposals to show how the infrastructure will enable an eco-town to adapt to climate change via: reductions in the heat-island effect; water and flood/drought management; increasing biodiversity; fostering local food production; and providing outdoor recreational and leisure spaces.
The composition of the panel was criticised by Landscape Institute president Nigel Thorne for not having a landscape architecture representative.
Landscape Institute climate change policy committee chairman Jon Lovell, who is head of sustainability at Drivers Jonas, shares Thorne's concerns. He explained: "A landscape architect can ensure that any schemes going forward fit appropriately within the landscape context. They can also ensure the design has an integrated and robust green infrastructure at its heart giving a strong sense of place and resilience to climate change."
Lovell said: "It is going to be difficult but not impossible.
"Eco-towns are, in principle, the best opportunity to realise true sustainable development that integrates economic, social and environmental performance. My concern is these schemes do not realise those principles.
"The fact that some schemes are of that questionable calibre reflects the highly varied levels of understanding that exist about the challenges of climate change."
The panel will meet again to give the eco-town developers chance to explain how they are responding to the recommendations.
- To read the report, see www.communities.gov.uk/publications/housing/challengepanelnotes.