Robert Stavins has expressed great pleasure with the outcome of the Paris talks. Yes, it does not guarantee more clearly the $100 billion per year fund to help poorer countries with their mitigation efforts, but clear goals and transparent mechanisms for moving to achieve them have been agreed upon by nearly 200 nations, with those responsible for 96% of world emissions providing more concrete plans for what they plan to do.
The loudest naysayer is climate scientist James Hansen. He declares this to have been all talk and "no action" as reported by The Guardian. Why? Because it did not include a carbon tax. I have already argued that this was not remotely on the table and is not even necessarily the best plan. In fact, as I forecast would be the case if there was agreement here, it has encouraged international trading in carbon permits. This already exists in the European system and China is implementing one in 2017. There are many arguments for this, which I have already laid out here before.
The agreement looks about as good as could be hoped for. Non-economist Hansen declaring the carbon tax to be the only acceptable action is just making a big fool of himself. He should stick to climate scence.