The number of megapixels determines the resolution of the images captured with the main camera. A higher megapixel count means that the camera is capable of capturing more details. However, the megapixel count is not the only important element determining the quality of an image.
A BSI (backside illuminated) sensor is a camera image sensor which captures better quality images in poor lighting conditions, and offers better overall sharpness and image quality.
The lens is made by a reputable photographic equipment manufacturer, as opposed to a low-cost unbranded lens.
This allows you to manually set the ISO level.
Optical image stabilization uses gyroscopic sensors to detect the vibrations of the camera. The lens adjusts the optical path accordingly, ensuring that any type of motion blur is corrected before the sensor captures the image.
CMOS image sensors are slowly replacing CCD sensors, due to reduced power consumption and better image quality. They can be very compact and cost relatively little to produce.