Warm supportive culture, embraces autonomy and diversity, full of elite talent
Pros
I've been at Facebook for 6 months. I've never been one for loyalty to my job or my company, but at least in Social VR, my team are some of the most genuinely supportive and caring people I've ever met in my life and I really feel like they accept me and will be there for me both when I need things at work and when I'm having personal difficulties. I'm given full autonomy to pursue the things that I think are most important. My team is incredibly diverse (including transgender, black, Asian, Pacific Islander, Latino, and an unusually high percentage of women) which shows both an extraordinary commitment to diversity and gives me faith that the product will be built to serve diverse customers. And the backgrounds of the people on my team are shockingly elite, with many projects on their resumes that are immediately familiar to and admired by me. I'm also proud that Facebook has so many people at the very top who are strongly committed to VR - like Zuckerberg's ambitious announcement at OC4 that his goal is to have a billion people in VR.
Cons
Facebook is hugely committed to transparency and authentic identity. So if you value separating your personal life and work life, don't want to share your personal feelings with coworkers or hear about theirs (or offer emotional support), or don't like to share with other people in the broader company what you're working on, it may be a bad fit for you. Likewise, if you prefer to be directed by leadership rather than establishing your own direction autonomously, Facebook might be a bad fit for you. Finally, Facebook's primary Menlo Park campus is located in the middle of nowhere with very little else around - you eat and get all your services on campus, with the nearest downtown a 15 min drive away. If you prefer to be in an urban center, you should either consider a different location, or a different company.