Ask HN: Working at Facebook. First hand experience?

Hi,

I've heard vastly different opinions when it comes to working at Facebook in an engineering position: some people say it's literally the best job ever because of the freedom, quality of coworkers and environment. Others instead said it's a highly competitive place (to the point where you're going to have a very hard time if you don't work 12 hours a day and aren't extremely smart) where you are worked to the bone until you naturally burn out and are then let go after a minor mistake, forfeiting your fat RSU package.

Do you have first hand experience? I am currently talking with a few big SV companies and I would like to avoid taking the wrong decision, so the more data points I have the better.

Thanks!