The Google Pixel phone features a very sharp lens. The lens optics serves an important role in determining the image sharpness and among of details the lens can resolve for a given sensor resolution. Some phones employ more aggressive sharpening in post processing to give the make it look sharper, but these can lead to image artifacts that can make the image even look unnatural.
The Google Pixel rear camera lens is constructed of 6 lens elements that produce a sharp image with low distortions. I don't know who is the manufacturer of the Pixel rear camera lens, but after viewing some 100% scale crops on DxOMark, we can clearly see that, at least in daylight, the Google Pixel outperforms the Samsung Galaxy S7 and Sony Xperia X Performance in the image details test, only outperformed by the HTC 10 in their test. I can clearly see that it's not in-camera sharpness that makes the difference because the fine details are there.
DxOMark also mentioned that the camera performs great in low-light and was able to maintain fine detailed, especially when HDR+ was used.
The Samsung Galaxy S7 image, which has also 12MP resolution, looks a bit washed out and you can clearly see that some of the fine details are lost. The HTC 10 is tack sharp, but the Google Pixel camera performance is almost equal to the HTC 10 in terms of sharpness.
People who like editing their photos in photo editing software will have more cropping freedom, as you can crop part of the image and still be able to get a sharp image to share online or make a large print from.
The HDR+ feature helps in preserving details in dark shadow and very bright areas, which otherwise would just appear flat.
I love looking at sharp images, especially when I zoom in on the phone and want to get a clearer look at a specific part of the image. This is why the sensor resolution doesn't tell us the whole story about image quality. A good lens is needed to optically resolve those details and it needs to have a high-resolution sensor with large pixel that can capture more data from the light, to allows capturing those fine details - the Pixel camera have them both.