Ricoh G900 has a 20.0MP 1/2.3
(6.17 x 4.55 mm ) sized BSI-CMOS sensor . On the other hand, Panasonic ZS3 has a 10.0MP 1/2.3-inch
(6.08 x 4.56 mm ) sized CCD sensor .
Ricoh G900's sensor provides 10MP more than Panasonic ZS3's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the G900 and ZS3 sensor size comparison.
Ricoh G900 and Panasonic ZS3 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.