Aw, look, it really depends what you're comparing it to. I just bought one on the weekend (at last!), and replaced my Canon G9 with it - but I'm not going to sell my EOS 1D MkIII.
The Epson is a really, really good SMALL camera, with the ability to use extremely nice lenses; the G9 is a little laggy, very noisy at high ISO, and a bit mushy for detail even at 100ISO. I'd rather have sharp, sharp glass on 6mpix than 12mpix of mushy detail, y'know what I mean? The end result in print would be similar (though with more defined depth of field on the Epson, of course), but with the R-D1, I'd have got the shot when I pushed the button, not a second later - assuming I remembered to focus, of course!
Compared to even Canon's 1000D, or 450D? They'd probably both leave the Epson for dead; but then it's a question of how you like to work, and how much you want to carry around, rather than (to some extent) the final results. If you like the experience of using a rangefinder, a dSLR isn't that. If you don't much care which you use, but want ultimate quality at the end of the day, well...a Canon / Nikon body with good glass in front of it may be the better bet.
Hope that helps,
R!