I work with a lot of ex-Facebook folks. In general, they speak highly of it.

Positives: Teams are fairly autonomous, platforms are stable and support experimentation pretty freely. Great for product/growth oriented hackers. Titles are hidden so you can walk into a room and be talking to a Director and have no idea.

Negatives: The backend is pretty abstracted away so as an engineer, you aren't encouraged to dive deep into the stack and see how it works. I've seen eng leads and managers operate with surface level knowledge of the backends that they work on. Going to startups or less mature companies will require a lot of learning to go deeper down the stack.