ALL MEGAPIXELS ARE NOT EQUAL
One common misconception is to take Megapixel count to directly equate to sharpness and resolution. While that may be true if the size of sensors being compared is equal, the other measurement you should be looking at is pixel pitch, which is the size of each light-capturing photosite on the sensor. The larger the photosite, the more light captured (and so image data) which typically means a greater dynamic range. Also, less heat is generated, which means less digital noise, especially at the higher ISOs.