Samsung NX2000 has a 20.0MP APS-C (23.5 x 15.7 mm ) sized CMOS sensor . On the other hand, Panasonic S1 has a 24.0MP Full frame (35.6 x 23.8 mm ) sized CMOS sensor and features Venus Engine processor.
One other difference between these two cameras that is worth mentioning is that Panasonic S1's sensor doesn't have an anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the NX2000 and S1 sensor size comparison.
As seen above, Panasonic S1 has a 2.3x Larger sensor area than Samsung NX2000. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.
DxOMark Sensor Scores
DxOMark is a benchmark that scientifically assesses image quality of camera sensors. It scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Samsung NX2000 and Panasonic S1 sensors have been tested by DxO and the results show that S1 has a better overall score of 95, 20 points higher compared to NX2000's score of 75.