I went to Syria three years ago. We combined it with a East-Anatolia visit, so we flew into Van, went to Diyarbakir, Nemrut and Sanli Urfa. From Urfa we took a Minibus to the border (there is one) and we walked across the boarder. Then I think some guy took us to a busstation and from there we continued to Raqqa, which is an ordinary city without any sights. Well anyway from this city we started our tour. Syria has a good bus system - you can easily find connections. We spent one week there and we saw a lot. Great place!!! One thing I want to recommend because I will never forget this in my whole life. The first bus we took was for a ~ 150 km distance. When we entered the bus I was very thirsty so I almost finished the 1,5 liter bottle of water I had. After 30 minutes the feeling started - the first stop was about 3,5 hours later....
You know if there was any tree in between these two cities I would have communicated with the driver (with hand and feet) but there was just flat land - there was nothing I could do. No gas station, no restaurants - no fu....... nothing!!!!!!!!

Syria is very interesting! Have a great time!
I think you should not miss: Palmyra, Maalula and Hama