I joined Google 2.5 weeks back. So may be its too early to answer this question. But still want to share my experience. As a computer science student, Google was always my dream company. So working in Google HQ is like living in the dream for me as of now. Here you can work with the best brains around the world, can use latest technology and tools. Even being a noogler (new Googler) you can be part of cool future projects that are yet to release.
Work environment is very friendly and all teammates and managers are helpful and supporting. Though it may take months to fully understand Google architecture, but you can access the codebase from inside and feel it how the features you always use are actually implemented. Company culture is to encourage and support new ideas (eg: google 20% time project).
Working in headquarter gives you the opportunity to see and listen to big personalities like Larry Page, Sergey Brin, Sundar Pichai etc in person quite often. Joining events of Google in person is of course very exciting (I am waiting eagerly for Google I/O 2016 :) ).
And it is a free world. Free food, free laundry, free gadgets, free massage, free gbus with WiFi. Have to mention the Google food explicitly. Breakfast to dinner, various cuisines are served in different cafes and its so yummy that almost every noogler really gains at least 15 pound after joining. (Famous 15 pound joke :D). Candies, chips etc are stuffed in each and every building. There are plenty gyms, playgrounds, volley ball court, different indoor games all around the campus. There is even a Indian restaurant in campus (that's right, not cafe, a free awesome restaurant) which being an Indian is my favorite so far.
Only problem with working in Google is that there are so many excellent people around, often you can feel very small. But actually I think it's a great opportunity to learn from these people. Overall for me its very challenging and that's the charm. :)
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