Facebook actually cares about keeping their employees happy
Pros
Of all the places I've worked, Facebook is the best at keeping their values consistent across the organization. They incentivize positive behaviors and spend money on things that actually improve employee health, happiness, and job satisfaction. Their goals are clear and they are consistent in applying policy while allowing reasonable room for variation. Leadership strongly emphasizes avoiding bias, treating everyone equally, and creating a positive environment, and that has a very clear positive impact at every level. As a woman in tech this is by far the most welcoming/comfortable place I've worked.
Cons
Like any software company with a lot of recent college grads (and especially one that places a high value on transparency), there can sometimes be a bit too much handwringing about culture and values and long, circular discussions on whether something does or doesn't fit the culture/values. But it comes from a good place, and again the company leadership do actually support those values and incentivize following them. Also, because 'working hard, contributing useful work and accomplishing things' are heavily incentivized, good people tend to be very busy. For a big tech company work-life balance is pretty good, but it is easy to load up your plate with way too much to do, or it's sometimes hard to get time with your manager because they've done that.