The six-day meeting of senior officials in the former West German capital was meant to lay the groundwork for the annual round of ministerial-level UN talks in Lima in December.
In turn, the Lima forum must pave the way to a historic pact which nations have agreed must be signed in Paris next year, to curb planet-altering climate change.
But some negotiators and observers expressed concern that the Bonn talks focused too much on restating well-known country positions on how responsibility for climate action must be shared.
"We will clearly have our work cut out for us in Lima," said Ronald Jumeau, spokesman for the Alliance of Small Island States (AOSIS) - the very countries at high risk from climate change-induced sea level rise.
And he warned "there won't be an adequate deal unless" developed countries give details of financial and expert support for the climate mitigation and adaptation plans of poorer nations.
David Waskow, climate expert at the World Resources Institute environmental think-tank, told AFP that while the tone of the talks had been constructive, "there is nervousness that the pace is somewhat slow.
"The pace needs to be stepped up to get to where we're going," he said.
And Alden Meyer of the US-based Union of Concerned Scientists said: "People are starting to panic a little" at the mountain of work still to be done.
The Bonn talks were meant to make progress on identifying the information that countries will have to provide next year when tabling their individual pledges for curbing Earth-warming greenhouse gas emissions - things like which gases will be cut, by how much, and over which period.
That "information decision" must be finalized by Lima to give countries enough time to complete and present their offers by a loose deadline of the first quarter of 2015.
But negotiators in Bonn remain stuck on the broader principle of whether the pledges should include commitments from rich countries to support adaptation to unavoidable climate shifts in the developing world, and whether there must be numerical targets for financial aid.
The 2015 pact, due to enter into force by 2020, will for the first time unite rich and poor countries under a joint, legal commitment to saving Earth's climate system.
It will seek to limit average global warming to two degrees Celsius over pre-Industrial Revolution levels.
But countries remain divided on the legal form of the 2015 agreement, whether there will be a differentiation between the responsibilities of rich and poor nations, and how to assess whether national carbon curbing pledges are enough, combined, to reach the 2 C goal.
On Friday, a bloc of Like-Minded Developing Countries that includes major polluters India and China, called for "actual negotiations" to begin.
Time was being wasted, they said, on "conceptual, brain-storming-type discussions" rather than grappling line-by-line with the actual contents of the envisaged agreement.
Scientists warn that on current trends, Earth could experience double the targeted warming limit - a recipe for potentially catastrophic damage to the climate system.