Pro Immersive audio experience
The speakers on the Nexus 6P are better than your average phone speakers. First off, there's two of them, and they're facing towards you (which makes sense when you think about it). Because they are on different sides of the screen, in landscape they create a stereo affect (you can hear sounds start at the left and move towards the right). The clarity and volume are also better than most competitors.
Pro Good performance
The Snapdragon 810 inside provides a solid amount of power. You shouldn't worry about performance - the newer Snapdragon 820 isn't much more powerful (it doesn't need to be - phones are plenty fast already). Instead, the main advantage of the Snapdragon 820 is better power efficiency which allows for smaller batteries - leading to slimmer designs.
Pro Great display
The Nexus 6P has a 5.7-inch Amoled screen that is comparable to other high end Android phablets. At a resolution of 2,560 x 1,440 it has a ppi of 518. The Amoled technology provides very punchy colors, and doesn't illuminate black pixels (unlike IPS panels) making dark colors look better, and also reducing the minimum brightness for nigh-time use.
Pro Fingerprint sensor in a natural location
Unlike most phones where the fingerprint sensor doubles a home button, the Nexus 6P has the sensor placed about 3/4 the way up the back of the phone, right where users already have their index finger when holding it. It is not a power button - only a fingerprint sensor, and its tucked away in a convenient-out-of-sight place.
Con New charging port isn't backwards compatible
Old micro USB cables will not work with this device, meaning if you lose or break your cable you will need to buy a new one instead of using an old cable you had lying around. If you need to top up your phone away from home, it will be much harder to find a suitable cable initially.
Con Slippery without a case
The phone is very thin, has a flat back with curved edges, feels a bit heavy in the hand, and is made of Gorilla Glass on one side and aluminum on the other. Without a case or skin, it can feel like the phone is constantly on the verge of slipping out of your grip.