I've admitted before that I'm a church history dunderhead. Taking a class in historical theology this semester is helping, but I've got a long way to go. I've read maybe half of Calvin's Institutes in my life (along with some other smatterings of his writings), about half of which was one book of the Institutes assigned for class this week. I was left with the distince impression that Calvin wasn't writing to advance some system of theology. He was writing to explain the theology of Scripture, of which God's providence and sovereignty are key themes.
I'm not going to belabor what is little more than my opinion and impression, based on an admittedly narrow reading of Calvin. Just for fun sometime though, read him and see for yourself if you think he's defending a system or expositing Scripture. It seems plain to me that he's driven by the text. If anything, he's a bit frustrating at times because he refuses to go beyond the text of Scripture into logic and systematization, as he is so often caricatured as doing. Don't take my word for it (not that anyone would).