Valis is pretty much on track.
A systematic theology is essentially a comprehensive, logically consistent system of belief; in Christian circles, it generally includes specific positions on a variety of technical issues.
The JWs have no systematic theology, because they never reasoned out their beliefs; they just tinkered with them from publication to publication. One example is the nature of Jesus. Sometimes, he will be spoken of as a creature; other times, he's divine. Another example is the basis of the ransom. They will present various analogies to try to make it sound reasonable (the cake pan with a dent, the closed factory, the unplugged fan, two men on a balance, etc), but they will never actually give a reasoned argument, based on clearly stated assumptions, as to why the ransom is needed or has any value.
It's not really surprising that the JWs don't have a systematic theology; not only would it make it much harder for them to constantly change their doctrines, but none of their people (except possibly Freddy) ever had the education that would be necessary to produce one.