I have used ZM 28 and 25, and CV Skopar(LTM) 28 and 25, and Leica 24, BUT not Leica 28s: I still use Leica 24(sold the ZM 25), both CV(Skopars are great!), and ZM 28; the ZM 28 is very easy in hand, great contrast, great size(for moving about) and most of all, great FL, film and cropped digital.
Having some older Leica glass, I might agree that the 28/2,0 has a certain rendering because it too is of this "Old School(Mandler) Character", but Zeiss has a rendering that should not be discounted, at all!
While the ZM28 may not be praised as highly for its object, Zeiss did not produce a /bad/ lens at this FL. However great the CV 28 for its price, the ZM28 renders a bit more, ah, cleanly(distortion,CA,flare), thus more predictably and as expected. Good color and tone. I am not the reviewer type(saying exactly something about everything), but if 28 was my sweet spot, I might consider the Leica 28/2,0... not the newer 28/2,8.
I use the CV 28 for its size, the ZM 28 for its result. Compared to the ZM 25, it's got the air, color and tone from f4 up, with a tad less contrast below f8. Not knowing what you shoot, at this FL, the ZM 28 is not ugly, but speaks quietly(more quietly than one, well respected--and you must pay to read--reviewer felt his WA+mid-tele kit should[sic] afford). A truely plain dealer, this lens.
rgds,
Dave