This could be an important step to bring peace to Syria, but it leaves huge gaps which allow for impunity among the actors currently inflaming the conflict.
1. To take part in the cessation of hostilities, armed opposition groups will confirm – to the United States of America or the Russian Federation, who will attest such confirmations to one another as co-chairs of the ISSG by no later than 12:00 (Damascus time) on February 26 2016 – their commitment to and acceptance of the following terms:
I still believe that a policy of annihilation is not legitimate, even when focused on ISIS. The history of abuses pointed at Sunnis in Iraq & Syria reveals that there are communities which are vulnerable and have no other authority to turn to. If states like Russia, France and the US can get away with crimes and move forward without penalty or prosecution, then the same is true of other entities. It is not legitimate to prosecute a war of destruction in the name of justice. Of course IS must be defeated to a certain extent, and like other repressive states, it must be pressured into reasonable compromises and decent treatment of minorities.
I am not convinced that there is really a fog of war which makes it hard for states like Russia to pick out IS targets from others, and they have definitely wasted any credibility they had with some of their claims. However other states like Turkey and Saudi Arabia have similar credibility issues, and there is the nasty business of Qatar and the US also disseminating arms recklessly (or even explicitly against their proclaimed strategy of supporting "moderates). ISIS is not a CIA front but US & GCC policies, including arms shipments and the liquidation of the Iraqi state institutions, definitely were meant to destabilize the state with the understanding that Islamists would fill that space.
Iran, and its nominal proxies in Shia Iraq also play a huge role in making life hard for Sunni. The new Iraqi state is more legitimate than the Sunni Baathists, but the sectarian divide has reduced religious pluralism there. Iran suffered an invasion from Iraq under the previous regime, so it was almost inevitable that democracy in a Shia-majority state with inflamed sectarianism and a liquidated political class would turn the tide the opposite way.
This is actually a very strong case for engagement with Iran, Iraq and Damascus regarding ways to protect the Sunni minority which are largely courted by ISIS, and form the backbone of their state, having suffered persecution. These communities are usually infiltrated and blackmailed into joining ISIS, and they literally had no authority to go to for protection. It is very unreasonable to expect those Sunni to surrender even if they can be 'liberated' from ISIS' grip. With each new iteration of destruction, prospects for a peaceful outcome grow ever more dim - it will take decades to build confidence in legitimate state institutions, and an increasing level of care to insure that past abuses do not re-emerge and force a new conflict between people who are prepared to take up arms once again.