I can see why some people would say Castro's design is better, but to me Castro is "over-designed". The visual slickness gets in the way of actually using it. I'd say Overcast is actually better designed, because it is more usable.
But point taken. It uses less standard controls, certainly. I have nothing against standard controls, my issue with Overcast is more with alignment and layout (especially the alignment and layout of the podcast images, up there in a corner).
In the end my willingness to trade usability for graphic design might be slightly higher than that of many other people (at least those who care).