Back when they were flexing their muscle invading Iran, Kuwait, etc. and using chemical weapons both at home and against their foreign enemies they had a very large standing military. The first gulf war greatly reduced their military and the sanctions that followed made it difficult to build it back up again. I'm not talking about how powerful they were in 2003, but in the late 80s.
Two man differnces I see.
Syria is one of the worlds largest holders of chemical and biological weapons. More than Iraq
Syria has a much more advanced air defense than Iraq did. Such as Russia currently supplying them with advanced surface to air missile batteries.