The country is polarized, so I am just speaking from the POV of the center and left. You already can see on the left, that even as HRC runs for President, both she and Bernie have in various debates praised Kerry on foreign policy, even as they disagree radically with each other. You also see many people, who are not "us", saying he is the best Secretary of State in their life times -- or not disagreeing when others say so -- even those supporting HRC for President. (It is very possible to do/believe both)
It is pretty clear that on climate change and Iran, Obama supported doing what Kerry did, but gave each little chance of succeeding. On Iran, at many points, when it was on the verge of failing, it was "Kerry's", but it was always true that without Obama's blessing and willingness to back something that was more likely to fail than work and which was controversial he could not have done what he did. On climate change, though HRC wants to draw a line from her "hunting down the Chinese", that is campaign rhetoric. Kerry's comment at IU that he spoke of wanting to make climate change his signature issue when he spoke to Obama about becoming SoS and being told that the administration held out little hope for diplomatic success on that. Kerry's long ties to the Chinese on that issue, his respect for them and his inviting them to a meeting at his home in Boston. Somehow seems more likely to get a very proud people, with a very long history to meet to find common interests than publicly "hunting them down".
Another place where Kerry tried to accomplish something that seemed doomed to failure was Israel/Palestine - especially as President Obama had already supported the George Mitchel effort to do so. There are also stories in both the Israeli and US foreign policy media suggesting that Obama may give a speech on Israel laying out the Kerry negotiated plan for a two state solution that was not accepted by Netanyahu and Abbas. The idea is that putting it out could serve as a starting point for any future effort at a 2 state solution. Here, I suspect that Kerry was right years ago when he spoke of a narrow window for a two state solution. I suspect that years from now, Netanyahu will be seen as the man who prevented that possibility -- unless he is jolted into really backing a 2 state plan. Unfortunately, I think there is less, not more, support for that in Israel now than - say - a decade or two ago.
Even if he gets credit JUST for the Iran deal and the climate change deal, he is a top Secretary of State. Had Paris failed, like Copenhagen before it, the fight against climate change would have been seriously hurt -- especially as there is little reason to think that the US would do better in future conferences. Had there not been a deal with Iran, there very likely would have been a terrible war there. On a personal level, I think he will be seen as a man of integrity and a talented diplomat, who managed to be both persistent and well liked by his peers - a very tricky thing to manage!
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