You'll laugh, you'll cry, you'll drown, you'll wish you bought in 2012
Pros
I had 5+ years of pre-FB experience in tech and other industries, including others consistently in Glassdoor Top 10. I don't regret joining FB: - I've learned an incredible amount about a new tech stack and product management for ads in only a few months. Not all my peers are brilliant about all things (which is good, as I'm certainly not) but every one of them is smarter than I am about at least one thing, and it takes very little time to find out what. - Data and logic rule here -- not always, not entirely, but enough. There is enough of a culture of rigor to metrics that we still have a North Star when in the weeds. - The perks are great. I have gotten broken glasses fixed by the dry cleaner for only a low tax rate. The food is shockingly good for the scale of the cafes, and I'm impressed every day by the whole MPK service operation. - Workplace is much better than emails as a site for debate/discussion about what to do. Also a con, because it generates a game of how-should-i-react-on-Workplace all its own, and in a more public record.
Cons
Facebook is like Bitcoin: people in it ask when you bought in because it's the easiest way to find out how powerful you are without being rude. I joined within the last year, along with about half of the company. The contrast in the level of success of people who joined N years ago vs N-2 years ago is logarithmic for all values of N. At its current rate, I don't think I can advise anyone to join now, and after I vest, I'm not sure I will stay. Part of this is that the starting comp isn't very good. The vesting stock is, but the cash is fairly mediocre (less than previous jobs I've had at far less profitable companies), and vesting accelerates over time. This nets to you being paid much more than before, year over year. The much greater share of it is that opportunities scaling in the same pyramid-growth path means that anyone thinking of joining today can't expect any of the same trajectory that available 2 years ago, and maybe even 1 year ago.