I love shooting with my Leica, too.
But, for photography, I prefer the M over the R. To me, an SLR excels at "practical" work, and I prefer an SLR with "modern" features that contribute to that style of work. So, I use Nikons for SLR work. Just personal style, though.
Although physics still applies, there really is something special about Leica glass, whether on an M or an R, when compared to other 35mm lenses. For me, it's the balance between "character" and the science of resolution and contrast offered by the lenses.