Some may argue otherwise, but there has never been a true Google Phone until the Pixel lineup. With the T-Mobile G1 or HTC Dream, depending on where you live, Google worked closely with HTC to ensure the hardware and software fit together well, but didn't exert tight control over either. They essentially handed HTC the OS and held their hand as they built a phone around it. The Nexus lineup was only a bit different, in that they were to serve as testing, development, and reference devices above all else, with only the Nexus 5X and Nexus 6P achieving much success among day to day consumers. Pixel is different. Pixel is Google's bid at playing Apple, and if they really wanted to compete with iOS without relying on innovative and deep-pocketed OEMs, it's something they may have been better off doing all along.
Since the beginning of the platform, Google has had issues with fragmentation, updates, bugs, and inconsistent software experiences. All too often, somebody would pick up a cheap or old Android device expecting a winning smartphone experience, only to be sent running to the nearest Apple store. While those who never get to experience the platform's best moments are a tragic subset indeed, their refusal to tolerate the results of the inherent flaws to Android's open business model is exactly the kind of attitude Google is displaying in creating the Pixels. With most Android devices, consumers are compromising something; in picking up a Nexus, they're compromising hardcore premium features and a status symbol. Those who pick up manufacturer-skinned devices are giving up a pure and seamless experience. Those who pick up a Pixel, Google hopes, won't feel like they're compromising a thing.
While policing the Play Store dutifully and preventing sideloading are off the menu for Pixel phones, Google designed the hardware from the ground up and allowed HTC to build it for them, and nobody but Google touches the software running on a Pixel device. If that sounds suspiciously like the way a certain tech giant in Cupertino operates, that's because it is pretty alike. Google is adding in premium features and keeping the software tightly integrated and frequently updated. If bugs or security holes crop up, count on them being squashed. If new Android features hit upstream, expect them to hit your phone very, very soon. Such things shouldn't be all that common, though, because Google hand-designed all of the hardware, hand-wrote all of the drivers and software code, and handcrafted the cohesive experience that those factors make up. This is the first time Google has ever done so, and while this is their long-awaited entry into the premium smartphone market as a creator rather than a software provider, part of the point of this phone is to light a fire under OEMs to help fight Android's core issues. While it can be argued that this won't help as much as Google seems to think it will, it's a definite step in the right direction.
Keeping a tight leash on the hardware and software of the Pixel phones, and presumably their future contemporaries, allows Google to present an unabashed, unadulterated Android experience of the sort that consumers have been sorely missing since 2008. Google is finally working to accomplish what most Nexus buyers have wished for, and what they probably thought they were buying when the first bold Nexus users picked up their Nexus One units. This is probably more than an experiment, since Google has spend untold amounts of time and money here, millions on marketing alone, but then again, everything Google has done since Search has been an experiment in its own way, so only time will tell if the Pixel lineup will stick around.