Pros
The people at Facebook are smart, creative and very approachable. The company has an open and horizontal work culture which makes it easy to have discussions across teams. The perks are awesome and it's always exciting and rewarding to go to work every day. The internal tools are great and the way that the company uses Groups, internally, makes it easy to ask colleagues for solutions to issues you might be facing in your work. Also, I had the best experience with the Facebook recruiting team, they really care about you as a candidate and their communication is efficient, kind and transparent. Overall, a really amazing place to work!
Cons
Not really a major issue, there's always a lot of stuff happening so sometimes it can be hard to focus on your work. You need to develop good self-discipline to prevent distraction, especially if you come from a very corporate work environment.