Gareth Porter has written a detailed analysis of the P5+1 negotiations from an Iranian perspective. A version of his piece was originally published in Le Monde Diplomatique, but I recommend the original version of the article, which can be found here.
Porter explains that the failure of the uranium enrichment swap must be understood in the West not as a result of Iranian dishonesty or internal political divisions, but a rational, calculated decision by the Islamic Republic that the proposal did not serve Iranian interests. He says
Objections to the plan all reflected recognition that the ElBaradei draft would deprive Iran of the bargaining leverage they have so painfully accumulated in the form of its LEU stocks. Senior Iranian national security officials had acknowledged in informal conversations that their main purpose in accumulating low enriched uranium was to compel the United States to sit down and bargain seriously with Iran. They had observed that, in the past, before the enrichment program began, the United States exhibited no interest in negotiations. From that strategic perspective, Iran is now in a position to negotiate with the United States in a way that it was not under Rafsanjani and Khatami, thanks to its LEU stocks.
Porter is concerned that the Obama administration plans to use the P5+1 offer as evidence of its attempt at “engagement” and as an excuse to move on to the familiar path of sanctions, threats, and indefinite hostility. Porter concludes
It now seems certain that the G5 plus 1 will declare an end to the negotiations before the end of December and move to the next phase of sanctions. Thus the talks with Iran will have ended without having attempting to explore the possibility of a larger bargain with Iran. That would have involved an end to overtly hostile U.S. policies and a symbolic recognition of Iran’s legitimate interests and status in Middle Eastern politics. That the Obama administration did not even try, despite Obama’s commitment to diplomatic engagement, is partly due to the desire of Samore and other advisers to try to impose a diplomatic solution on Iran that could be portrayed as a diplomatic victory over Iran, even if only in the short-term.
— Ben Katcher