I loved the amount of impact and ownership I was given as a Data Science Intern. At previous internships, I'd worked in both business and software engineering roles, but my intern project was generally a small, isolated effort and had no impact on the actual company or product I was a part of. At Facebook, I was directly embedded in the product decision-making process, helping to provide actionable insights and recommendations. My manager directly put me in charge of analytics for a segment of our team's product. By the fourth week. I was responsible for providing information and recommendations for that segment to other team members. Because I was so product-focused, the internship isn't nearly as technical beyond writing Python data pipelines and SQL queries, so if you're considering software engineering as well, that's something to think about.
Facebook was a great place to work. They really make an effort to give you a project that you can finish while you're there and a project that will ultimately get used. Facebook also treats you as a full time employee, so you have access to all of the same perks as the full time people, which includes the free food, shuttles, gym, and most importantly, the weekly Q&A with Mark.
There were also a lot of intern-specific perks, like Q&As with other important people in the company, like WhatsApp, Instagram, and Oculus founders, and trips to see plays and baseball games in SF.
Most of what I disliked about my experience had to do with my manager, so I wouldn't count it against Facebook internships in general. My manager wasn't great about giving feedback in our weekly one-on-ones, so I was never sure whether I was living up to Facebook's "work fast" motto. There are also two performance assessments during the internship that determine whether you get a return offer, so I felt a lot of background stress leading up to those given that my manager couldn't/wouldn't give me useful feedback. Everything turned out fine in the end so the stress seemed kind of unnecessary.
For what it's worth, Facebook internship stress was not as bad as Princeton undergrad stress. At Facebook, I stopped thinking about work when I got home and on the weekends, whereas at school, the stress and deadlines are with you all the time.