Meta

An amazing amount of resources (including a completely open & greppable codebase) for engineers to teach themselves just about anything.

Really awesome internal tools.

Unbelievable compensation & perks.

The company trusts & believes in its employees.

You become associated with the Facebook brand.

Also a con, but you have a ton of freedom in what you work on.

The tl;dr is Facebook is a big company, and its cons reflect that. The company mission and values are incredibly admirable but have become increasingly difficult to implement as the company has grown.

• You might find yourself working on a project with over a million lines of code, but nobody on your team has written more than 10,000. The need to sit down and figure it out yourself can be pretty stressful in an environment that is pushing you to "make an impact" and be constantly shipping new features.
• The few senior engineers (in my org at least) show little interest in mentoring more junior engineers.
• Sink or swim mentality among engineers; the mega-teams supporting products in the core app can be brutal and unwelcoming.
• Launch decisions are very political. The criteria for launching a change is opaque, and feedback from department leads happens far too late in the development process (often in the meeting where a launch decision is being made!). Little has been done to fix these issues despite it being constant feedback for the past year.
• Performance reviews put too much emphasis on immediate personal output rather than collaboration and assisting other teams. This causes teams and individuals to focus inwardly. While it's never been malicious, I've seen this behavior directly harm other team's productivity or metrics.
• Work/life balance is below average on the day-to-day, but on-calls are truly awful.
• Decision-making has become a bit too distributed between orgs and reflects in the overall product.

Pay close attention to teams that have poor retention and take drastic measures to reverse the vicious cycle. The less seniority on a team, the faster the turnover rate becomes.

I think there is a gap between what's best for the company and what is rewarded in performance reviews. Fixing performance reviews, starting with incentivizing mentorship and collaborative behavior, will likely fix many of the current problems at Facebook.