No, it's not CoD5. It'd be like, CoD 6 or 7, depending on if you count United Offensive as a stand-alone game or something. You had CoD, CoD: Finest Hour, CoD2, CoD:BRO, CoD: Roads to Victory, CoD3, CoD:4, CoD:WaW.

Then MW2.

It's not even techincally the fifth game if you go by PC only, instead of console related games. It'd be the sixth after United Offensive.