Nice job, especially considering the lack of established material you had to go on. Only crits I have, and they are minor, is perhaps a little less detail on the limbs. Though it may go against your modelling ethos, a plainer, smoother surface on these areas would be more fitting with the 50's feel. To be honest though, you've done a great job of embelishing the model without taking it too far. As for Zbrush, I never got on with it personally, finding it bloody hard to get to grips with. I think I've been indoctrinated by Autodesk as I was able to leap straight into Mudbox and haven't looked back since. I also found Blender just as hard after years of using 3dsmax.