The camera sensor seems to be the same one as the one they put last year in the Nexus 6p and 5x, but the new phones have gotten a major upgrade in image processing performance and in software. They also benefit from a new gyroscope that's used for seemingly very good video stabilization (not clear if it's used for still photos as well). Oh, and it has a faster shutter speed.
Hopefully next year they use an f/1.8 or wider aperture, too.