Pre-era was a bunch of elite college kids who were in the right place at the right time, in the right business, technical and social environment, to create a masterpiece. Such an intersection of factors is unlikely to occur again. (If for no other reason, that we likely have about 20 years left on this planet.) Omid Kordestani was the adult in the room at the time, and he let the kids run feral. It was probably as much his style as it was that he was already successful (in the SV sense) and relaxed.
Then you have the Eric Schmidt / George Reyes era. Reyes was from Lifelock, which tells you his caliber. But, a good team for an IPO. Lucky for Google, Hal Varian was there too.
They outgrew Reyes and hired Patrick Pichette, formerly from McKinsey and Bell Canada. I think it's often overlooked that he came from a monopoly and Google was on its way (and desire) to become a monopoly and of course sought to avoid even the light touch of the Clinton Justice Department (I refer to the MS anti-trust case).
All through this time, everyone and I mean everyone wanted to work at Google. They were big enough to be a real company but not yet big enough that beers and toys weren't a fixture around every corner of every building. It was still a work hard, play hard culture and (outside of AdWords and classism that was starting to arise out of red badge ism) technology driven and egalitarian.
Under Pichette they bought Motorola for the patent portfolio and a culture of lying to the public, and most importantly internally to employees began. To be fair, the lying was required to pull off the Motorola strategy, but it was at this time that the us (executive suite) vs them (middle mgmt and ICs) really began. It was then that the Google became IBM. BTW, if you met any Googlers of this era, you were more likely to find them to be full of themselves than googlers of previous eras which is ironic because these googlers were replaceable cogs, vs earlier googlers.
So, with IBM^H^H^HGoogle now wearing big boy pants they needed a real CFO, one that could believe his own bullshit when entertaining bankers (who believe their own bullshit). Google was now so powerful and wealthy that the compulsion for more power and more wealth was all consuming. When you're on top, you want to stay on top and you maneuver to do so. Google was already a technology powerhouse but that wouldn't be enough. Do keep in mind that Schmidt had/has aspirations of true political power, so this surely was a guiding force in this evolution. (And besides, the right move considering the goals.)
So they brought in a CFO's CFO, a true Wall Street player. Then they formed Alphabet. Why, oh why? To bring costs under control. Google doesn't care about costs. A few million here, a few million there, the technology playboy dream team don't care about such insignificant sums, but Wall Street does. So Porat maneuvered them into this awkward structure so that she could trim fat. And boy was Google fat.
Oh, and she removed don't be evil from their vocabulary. Very, very smart Wall Street move. Of course Google had always reserved the definition of evil for themselves to make, but this needlessly tied their hands or at least caused contortions when exploring the most lucrative market of all -- China. To be fair, Porat was right. Google is a megacorp. Megacorps should not have morals as such and they should indeed pursue all revenue (and tax structures etc.)
Internally, it became very hard to just start a project on a whim. Budget had before been of little concern, now it became primary.
There is still resistance and some inertia. I find it very very interesting that Google Home, a project doomed to failure from the beginning, was allowed to happen and is still allowed. And that Nest is still completely mismanaged. I believe this is because Porat is not a technologist. The obvious synergies that I see with those products, and the Google/Android ecosystem, aren't visible to Porat.
So you can see, Google is now a finance-driven company, not technology-driven. Starting in 2015.