By retiring early, he sorta let Google, this still immature organization, get completely steamrolled by the board. I used to work there and the culture shifted rapidly upon his departure.
First was the elimination of TGIF, a weekly meeting where Larry and Sergei would come out in the flesh and answer some of the most politically sensitive questions you could imagine right there at 1600 Amphitheatre Pkwy, second was the rule of CFO Ruth Porat who eliminated many bets and turned Google into a lean mean ad selling machine. Sundar Pichai seemed too distant or disinterested to fully engage with Googlers or fight for their interests. For example, his first order of business was to take over one of the three buildings off Charleston and make it off limits to mere mortals. Maybe that is good for share holders, but it wasn't the Google I ever signed up for.