Maybe I am be wrong, but of all viewfinders I have seen (and I admittedly haven't seen the H3D) I preferred the R8/R9 for manual focusing. Note that some are brighter, but none were better for focusing. So, I expect Leica to make no mistakes here. I do prefer the R8 to my Contax 645, specifically. The latter is larger, but it was easier to focus the R8.
In fact, there are people here who have seen and held the S2 at Photokina. Did anyone try manual focusing with it, and can compare to the H3D? That is probably the acid test here.