It's the worst lens I every used. I was so unimpressed by my RB lenses (50, 90, 180 all C versions) that I sold my whole kit. I may have just stumbled on some poor samples of these lenses. The RB is a great system camera, but my lenses left me looking for sharper and higher contrast options (just my particular taste in things). On the other hand, I've seen some very wonderful images made with the RB. To each his own . If you prefer really sharp, you'll have to look elsewhere. The RZ lenses, for example, are much sharper generally. I'm not sure if you can use RZ lenses on the RB though.....
I am just as impressed with its image qualities as I am by any quality optic. I used it quite a bit before I got my own RB camera (an RZ model one), but I never got my own because I like the focal length and the maximum aperture of the RZ 110mm better.
If I had an RB, I'd probably be more inclined to either go down to a 75 or up to a 127 for my "standard" lens. Strangely enough, while I love a normal lens for 35mm hand held shooting, I don't seem to care for them that much in the larger formats shot on tripods. I generally prefer a standard lens that is either slightly long or slightly wide when using the larger formats. For instance, a 105mm on 6x6, or a 210 or 240 mm on 4x5, or the 55mm on 645.
"Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."