When the first pictures of the G10 appeared on web, I liked it immediately. Its classic rangefinder-style design appeals to serious shooters. In real life it looks (and feels) every bit as good. Build quality is very solid and finish is nice (click on the image to enlarge). It is reasonably heavy to hold it steady, but not too heavy to carry all day in a jacket pocket.
Ergonomics is good and I especially like the new exposure compensation and ISO selection wheels. Very handy!
The new high-resolution screen is just gorgeous, and pictures look better than in real life, no kidding! It reminded me Apple iMac glossy screens, which I didn't like because of too much reflection, but for a small camera screen it doesn't matter. The viewing angle is very wide and it compensates a bit the fact that screen is not flip-out.
About image quality. Does it really have 14 megapixels? Good question. I compared my old Powershot G5 (5MP) with the newer A720 IS (8MP) and didn't find any difference in detail, despite larger file sizes. Here the resolution increase is obvious. Not sure if it's exactly 14 MP, but under ideal lighting it may be close. Of course, this huge resolution comes at a price of higher noise. It is a problem of all compact cameras and the G10 is no exception. Noise reduction is visible in shadow areas even at base ISO 80. To make things worse, G10's default sharpening is way too strong, which in combination with noise reduction makes fine detail look coarse. I set sharpening to lowest -2 and saturation +1, saved it as custom colour and got much better results. Unfortunately, in-camera noise reduction cannot be adjusted and custom colours are not available when shooting RAW+JPEG.
Is RAW really necessary? Only if you shoot something very important and want the highest possible quality, or shoot at high ISO and want to apply better noise reduction. Otherwise, if you shoot at ISO 80-100 and care to set correct white balance and exposure, your JPEGs out of the camera will be as good as you can get from a RAW converter.
My only gripe about G10's image quality is very pronounced chromatic aberrations in 28-50 mm range. There is no way to correct them either in camera or in supplied software, which is too bad, rival cameras from Nikon and Panasonic can do that. I hope the lens profile will be included in later versions of DPP program. In the meantime I'll have to use Photoshop 'Lens correction' filter.
Per pixel quality is not exactly as good as DSLR, but for prints it doesn't really matter and for screen preview 14 megapixels are just too much. I downsize photos to 8 MP and without sacrificing much detail get smooth and sharp pictures very similar to 20D. Photos taken at ISO 200-400 can be downsized to 5 MP with good results. As for ISO 800-1600, I think they are not usable for colour shooting at all. Though you can shoot RAW, convert to black & white and get pictures very similar to 35 mm film scans, not too bad :)
How does it compare to other digital cameras I used?
Canon EOS 20D One can say it is not a fair comparison, but I think it is. In terms of image quality, focal range and maximum apertures, the G10 is almost identical to the 20D and Sigma 17-70, my favourite walkaround lens. Worse high ISO performance is compensated by the image stabilizer, which can gain extra 2 stops.
G10 advantages: Better screen, faster preview, movie mode, small, light, quiet, non-intrusive.
20D advantages: Much faster and more reliable autofocus, faster continuous shooting, interchangeable lenses.
Canon Powershot A720 IS The G10 is simply better in every aspect. Its shorter lens (140 vs 210 mm) is compensated by higher resolution.
Canon Powershot G5 This is the most interesting comparison. How did the Canon's flagship compact camera change in 5 years?
G10 advantages: Much faster (start up, shutter lag, preview and everything), higher resolution sensor, large and higher resolution screen, wider lens (28 vs 35mm), no purple fringing, better ergonomics, more compact (lens is fully retractable).
G5 advantages: Faster lens (F2-3 vs 2.8-4.5), no CA and sharp corner to corner, flip-out screen, IR remote control.
I miss the last two features most of all and think dropping them was Canon's biggest mistake. It is possible to connect the camera to an external display and buy the optional cable release, but it would be not nearly as versatile and convenient. Even smaller but flip-out screen and IR remote could make this very good camera really great.