Hello,
unfortunately, the EVF is not compatible with the GR Digital III, but then again, the screen is pretty good (and the EVF is supposed to have a rather low resolution, but then again, I have not even seen the EVF in real life, so do not take my word for it).
You can however use external optical viewfinders (I would not recommend the Ricoh GV-2 though if you are wearing glasses, although the view through it is very nice). A lot of people on the net seem to use the Voigtländer 28mm finder depicted in this photo:
About the GR Digital III: it is the best compact camera in my eyes. Really. Considering how the lens performs and how good the handling is, I really cannot say otherwise.
I have also tried other compacts like the Canon G series (G11 which was the most recent model at that time), but I found the handling to be a bit clumsy. The lens is also a bit slower at f/2.8, but it comes with shake reduction and has 5x zoom if you need that.
The Panasonic LX/Leica D-Lux series also fit into the segment of high quality compacts, but I was disappointed by the lens as it has to be electronically corrected for distortion...The buttons are also a little bit on the small-ish side.
I have not tried the Olympus XZ-1 yet, but it seems like lens-wise it really is a serious concurrent to the GR Digital III...
So if you are looking for a really good lens in a very well-built compact camera (all magnesium-alloy body), I guess, the GR Digital III is a good choice (however, lens is a fixed focal one at 28mm equivalent, so if you really need a zoom, this is not the right camera for you). No distortion (except of in macro mode), very good corner-to-corner sharpness and quite resistant to flare and ghosting.
The sensor also delivers quite fine results (you have to shoot raw to get the best results, however), but occasionally you will get ugly streaks at ISO 800 and more often at 1600 because of banding issues.
I also love how you can customize nearly every aspect of the camera (like switching the green power button light off or assigning functions to buttons etc).
Here are some photos I made with the camera (all are processed raw files):
http://ricohforum.com/viewtopic.php?f=17&t=5960
http://ricohforum.com/viewtopic.php?f=18&t=5961
haha, what a shameless self-promotion
Full size and out-of-camera JPEGs/RAWs on demand