Here's my take on cell phone cameras. Yes there are ones better than others (S6, iPhone 6+, G4) but for what 99% of the population uses the photos for, any decent phone today will do. Most people are only using these photos on Instagram, Facebook, and other social media. They are not blowing them up and printing them. So yes, some cameras are better than others when zoomed in but rarely anyone does that in real life situations.
Keep in mind I said most. There is still a small % of the population who use them outside of showing on a cellphone/tablet/computer screen and social media but for most people even phones like the Moto X have good enough cameras for what they use them for.
With all that being said, the Nexus 6 camera performs amazingly for showcasing photos on devices and on social media.