Though the G3 technically can shoot as high as ISO 3,200, like many of its competitors its photos become unusably muddy starting at around ISO 800. Up to and including ISO 200 the G3's shots remain relatively sharp and noise-free; at ISO 400, it depends upon scene content and output size. For instance, you really wouldn't want to use it for something with a lot of detail, like this. But as subsequent samples show, it can be acceptable.
You can see the blurring effect the noise reduction has at ISO 400 compared with ISO 80, but at small sizes it doesn't matter much. (left, ISO 400, 1/10 sec, f3.5; right ISO 80, 1/2 sec, f3.5)
You can see the color noise at ISO 400 (left) vs. ISO 80 (right), but at small sizes it doesn't seem to have a detrimental effect on photo quality. (left, ISO 400, 1/10 sec, f3.5; right ISO 80, 1/2 sec, f3.5)
Given that it's small and uses folding optics, the G3 has a surprisingly sharp lens; like most ultracompacts, though, it tends to be significantly sharper in the middle than at the edges.
Like most compact cameras, the G3's lens displays quite a bit of barrel distortion at its widest angle, which is a not-terribly-wide 35mm equivalent.
The G3 displays a bit of pincushion distortion at its maximum telephoto, 140mm equivalent.
Lens distortion exacerbates a lens' tendency to produce fringing, which normally should only appear on very high-contrast edges. Also note the rather cool white balance of the G3's outdoor shots.