Aside from the huge screen and faster performance, the biggest and most notable difference between these phones is the camera. The Pixel and now the Pixel 2 really steps up the smartphone camera game. If the camera is a priority for you, we highly recommend making the switch.
The new Pixel 2 XL uses a large sensor with a f/1.8 aperture and 12.2 Megapixels. Google added optical image stabilization, electronic image stabilization, portrait mode, and dual pixel technology for stunning photos. Low light performance is some of the best on the market, and the auto-focus is incredibly fast. Not to mention 4k video recording, slow-motion video, blur effects and more.
Even the front-facing camera is better even though they're both 8MP. The Nexus 6P has fairly outdated camera sensor technology, and the lack of image stabilization really hurts the quality of photos.
The smartphone camera with the highest DxoMark score in history is the Pixel 2 XL. That's all you really need to know. You won't be disappointed by the camera on Google's new phone.