Russia doesn't care about isis, Russia cares about maintaining Assad, and thus maintaining the Russian naval base in Syria. that's it. that's all. that is the issue. Russia isnt like the US, it cant project its forces worldwide like the US can even without bases, because Russia doesn't have this:
https://en.wikipedia.org/wiki/List_of_current_ships_of_the_United_States_Navy
Russia needs that port. and they're clearly willing to fight for it. obama has effectively abandoned the free syrian army, if there ever was such a thing, to destruction. now there are two options in syria; a relatively secular, yet brutal, dictatorship, and an islamic-law based caliphate. good job obama, good job putin, another country damned to ****hole status.