John McGhie, campaigns and investigations editor at Christian Aid, expressed concern at what he saw as the summit's failure to properly tackle the issue of trade.
"Given that trade is the most important of the campaign's three aims, it is fantastically disappointing that they haven't done more, and have merely shunted it off to the World Trade Organisation meeting in Hong Kong in December," he said.
He described a "widespread disappointment" and added that some African delegations from the global coalition against poverty were "livid".
But Richard Bennett, chair of the co-ordination group, joined Bob Geldof in heaping praise on the summit's achievements.
"The way that people have taken up the issues of trade justice, debt cancellation and more and better aid has been inspirational," he said.
"G8 responded by promising debt and aid changes that will give hope to millions."
Steve Tibbett, head of policy at ActionAid UK, said: "Although there are some nuggets on debt and hints of progress towards cutting strings on aid, G8 has failed to deliver on trade."
But Andy Atkins, advocacy director at Tearfund, said dissent was natural with such a variety of voices within the campaign. He said: "Any comment on the summit needs to be interpreted according to the perspective of each individual spokesperson.
"If you listen to the climate change people, they're very depressed. But those working on HIV and Aids are much happier."
He added: "To be honest, it was about what I expected. Is it a complete success? No, but it's progress."