I know that when you were looking at the GXR, the M-module had not been released. I have a GXR, the EVF, and the M-module, and a bunch of tiny CV lenses.
Here is a sequence of completely uncorrected (apart from WB) images for a customer; all were shot at f8, using the CV 12/5.6,
The colours are accurate, the distortion is very low, and the great upside of that modular design is that you can put the camera right into the corner of any room, tilt the EVF up, and see pretty much the whole room with this lens. Focus (if you need to), press the shutter, step out of the way, wait for the timer to do its thing, and you're done. Unless you have tried to do this with (say) a Nikon D3/D3s or a Sony A850, this aspect might not mean much—but all the Live View in the world (D3/D3s) won't help you one iota if you can't see the LCD. And using right angle magnifiers on the OVF of either the Sony or the Nikon will not tell you critical focus. If you do use Live View (Nikon) and a Hoodman loupe, for example, the camera–tripod will need to be far enough out of the corner to let you get behind it—meaning the amount of any interior the lens will cover will be reduced.
Personally, the GXR is the most intelligently designed tool I have ever used, and this claim covers a lot of camera territory. It is also incredibly customisable, and all settings are really saved (is anyone at Nikon listening?). All settings may be recalled and edited after being saved, too.
The EVF and the LCD both use an innovative separate-button approach to the focus aids, which really work. F1 enlarges the image; F2 engages a Black/White full-screen peaking mode (on either the full, or magnified, image) and a half press of the shutter button returns you to full screen for final framing. It works, and it works well, and it's quick to use.
Is it perfect? No, it needs a better EVF, and you really can't use the LCD either for accurate image review for either critical sharpness or colour, but I do use the histogram—and now I know what the camera is doing, I trust it and have made some lovely images with exposure spot-on, too.
Only APS-C, and only 12Mp, but no AA filter, and truly excellent inexpensive lenses. It's not until you see the images on a decent monitor that you realize what detail the camera's capturing. And, according to Ricoh, this module has been optimized for WA lenses; this CV 12 looks as good (to me) as the 14–24 looked on the D3, and that's a very good camera–lens combination indeed. And the Sony APC-C 16Mp sensor is rumoured to be coming out soon in what will be called the 'A-16 M-module', but without AA filter, and that will be even better than the current one.
DIGLLOYD: Looks like yet another great ALLVIEW option for Leica M, Voigtlander M and Zeiss ZM lenses!.
Color: it appears to me that there is some modest bluish color shading in the corners, only to be expected since the Leica M8 and M9 are not free of this, even with lens correction.