The Lenovo P2 main camera can capture very sharp images in daylight, but even in good lighting conditions, there is sim loss of details due to the poor low-light performance of the sensor. Don't get me wrong, just take a look at the sample images taken by gsmarena.com,. Just zoom in at 100% scale and you can see that the images are super sharp, but you can still see noise apparent in the image that eats some of the details. So shooting in daylight will give you good quality image, but everything starts to fall down pretty quickly as you shoot in less of ideal lighting conditions, and I'm not just talking about night shots, even indoor shots with good light results in a soft images.
It's not a huge problem if you just intend to take image and sharing them on Facebook in low-resolution, but this camera is certainly not suitable for enthusiast photographers who are searching for a phone with a rear camera that can shoot great photos also in low-light situations (e.g. at night, indoors, etc.).
I did dig a bit deeper and found out (via gadgets.ndtv.com) that the rear camera uses the Sony IMX258 sensor. This is a 1/3.06" 13MP stacked image sensor (Exmor RS) with 1.12-micron pixels. More information about the sensor can be found on sony-semicon.co.jp (PDF file). Some website say that it's the IMX230 Exmor RS sensor, but it's not possible because that sensor comes in either 21MP or 16MP, not 13MP as clearly stated by the official specs on lenovo.com.
No doubt that the small pixel size and the the f/2.0 aperture lens doesn't help to improve it either. The IMX258 was released on September 2015, so it's quite old in mobile-phone terms.
So overall, the rear camera of the Lenovo P2 produces good images under (very) optimal lighting conditions, but overall I wouldn't recommend it for anyone who really love taking photos and don't want to limit its creativity by the poor low-light performance of that sensor.