The G12's image quality looks great at the lowest ISO sensitivities; you can start to see a slight bit of detail degradation starting at ISO 200 that becomes more overt (along with noisy) at ISO 400. ISO 800 is probably the highest usable setting under the most forgiving circumstances. Picky shooters really won't want to go beyond ISO 200.
The G12's images are nearly identical to the G11's; the slight differences you see here are more attributable to minor discrepancies in the elevation of the tripod head due to the temporal gap in testing.
(1/250 [G12], 1/320 [G11]; f4, center-weighted metering, ISO 400)
Processing the G12's files as raw doesn't deliver an unambiguous advantage over the JPEGs. The artifacts and colors are a bit different, and you might be able to gain a little sharpness from the raw, but it doesn't provide any shooting-exposure advantages.
Especially if you're used to shooting with a dSLR, the G12 doesn't feel very fast. But part of that's perception; it's certainly zippy enough to catch animals (this squirrel did not sit still for long).