I had a great time as an intern at Facebook
1) Work: This varies heavily with team, but you do have some say in what team you're assigned. In the Seattle office the bigger teams are Ads and Messenger. I was on Ads and the work was impactful and challenging but fun. Facebook also has amazing internal tooling, processes, and support; meaning we get to spend more time on meaningful work rather than dealing with trivial setup and issues.
2) Perks: FB definitely has one of the best perks among the top tech companies. There's the usual free food, mini kitchens, pingpong/foosball, and gyms, but FB also provides free housing on top of your salary, professional laundry on-site (includes dry cleaning), bike stipend, wellness stipend, a phone with an unlimited plan for the term, and a wide selection of tech equipment.
Also, if you are in Seattle, there are many chances to go to HQ (I went 5/6 times during my term). If you do, FB pays for the flight, hotels, rental cars, and food if you eat out.
3) Culture: Work life balance is great, everyone is very friendly and helpful (especially if you tell them you're an intern). There are many hackathons and intern events that you can take part in, as well as company-wide events, clubs, and learning sessions. Leadership is also great. Mark Zuckerberg is very transparent with employees and hosts a Q/A every friday where anyone can ask anything about the company.