Pros
There is no shortage of opportunities at the foundation. If you are proactive and don't get burned out (and have a decent manager) you can certainly create opportunities to grow and learn while you are there. But you will most certainly need to create them for yourself. If you come into the right role, you will have the world at your fingertips. What is said about the benefits and compensation is true as well. It's really a first class package and above any industry standard for many of the positions here.
Cons
As an individual who had previously only worked at small organizations, this was an eye-opening experience for me. I can only imagine that it must be akin to working in a massive bureaucracy or government agency. Everyone is on a different page here and things are constantly evolving at a rate that seems nearly impossible and certainly irresponsible. Restructurings of teams and strategy refreshes come rolling down the hill before teams are even able to get their feet under them. It's all quite MSFT-y in the culture and driven by a very, very old-fashioned, centralized, top-down management structure. Achieving any sort of actual results towards the mission within this environment is not impossible, but it certainly is the exception. Managers are not incentivized to manage, lead, or make decisions. They are all accountable as individual contributors, so at the end of the day they are looking out for themselves. Nearly everyone who walks through the door (and I will certainly admit I am not immune to this) is on the personal quest for their own significance as it relates to the mission. This can very often override the greater good and any sense of working as a team. The most important thing to know in all of this is that every dysfunction leads back to the founders themselves. Much of the problems are not solvable because of this fact. No one is able to have frank conversations with them. They dictate the culture at the very top and this drives everything else below. An annual results review meeting with each team is like presenting in front of a royal court. The weeks and months of churn and anxiety that lead up to these meetings are astounding and this is just one example. Bottom line: go there for the opportunities, go there for your own career, but don't go there expecting to actually contribute to social impact.