A little after that. I'd put the heyday between 2003-2010, starting with the GMail launch and ending with the Chrome & Android launches. That period includes GMail, Maps, Scholar, Orkut, Reader, the acquisitions of Blogger/YouTube/Docs/Sheets/Slides/Analytics/Android, Summer of Code, OAuth, Translate, Voice Search, search suggestions, universal search, Picasa, etc. Basically I can look at my phone or computer and basically everything I routinely use dates from that period.

Agreed. I remember the town hall meeting where they announced the transition to being Alphabet. My manager was flying home from the US at the time. He left a Google employee and landed an Alphabet employee. I know it was probably meaningless in any real sense, but when they dropped the Dont Be Evil motto, it was a sign that the fun times were drawing to an end.