I'm in the same boat (not the one floating through the sunken city, though) when it comes to background (or lack there of) for Joe Golem. And, after reading the 5th (and final) issue for this current run, I'm still left feeling like there's so much not yet explained (or even hinted at), but also not sure if it's worth my trying to find it out.
If/when a new Joe Golem limited-series appears again, I'll have to decide then if it's worth buying or not.