Nobody Controls Syria

Syria's fate in its five year old civil war is still very uncertain.  As the open source map curated by the Carter Center demonstrates, the government, opposition forces, ISIS and Kurdish dominated YPG groups all control comparable amounts of habitable Syrian territory.

The YPG controls most of the territory along the northern border, opposition forces and the government control a roughly equal patchwork of territory along the coast (although the opposition forces are themselves divided among multiple factions) including a few small areas where there are ceasefires in place, and ISIS controls most of the habitable areas of the southeastern part of the country.

About half of Syria is basically uninhabitable mountain and desert territory not really controlled by anyone.

The Syrian government appears to be gaining ground with Russian backing, but still controls only perhaps 1/8th of the nation's territory and does not even have firm control over its leading city, Damascus.  It is largely restricting its efforts to defeating opposition forces in the coastal areas that are not controlled by the YPG and has made only modest inroads against ISIS (in part by design with the hope that ISIS will harm rebels and will be defeated by others).  Given the government force's relative unity and far superior weapons compared to opposition forces, its failure to be more effective is remarkable.

ISIS, of course, which spans both Syria and Iraq, faces concerted coordinated attacks from the U.S., its allies, Kurds, the Iraqi government, Russian forces and Syrian forces.  These attacks have destroyed a large share of their conventional heavy weapons like tanks, armored personnel carriers, artillery, and aircraft.  These attacks have also destroyed many ISIS bases and ISIS has lost thousands of fighters in the war that has been ongoing since its inception.

ISIS probably has no more than four operable warplanes which have proven difficult to deploy without being shot down, has limited numbers of anti-aircraft missiles, 100 or fewer tanks, a couple dozen self-propelled artillery pieces, and perhaps one or two hundred other armored vehicles, and hundreds or thousands of pickup trucks with mounted heavy guns.  A concerted attack on a convoy after ISIS lost Fallujah destroyed a substantial proportion of its heavy conventional weapons.

But, the people who are being "liberated" by Iraqi and Kurdish forces are mostly Sunni Arabs who have little interest in being a part of Shiite dominated Iraq or Kurdish autonomous areas within Iraq or Syria. So, gaining control of more territory is a non-trivial matter despite numerous military defeats in Iraq and Syria for ISIS.