Pros
Impact: Wikimedia runs Wikipedia, it's a non-profit on a mission to share the world's knowledge. Your work is supporting volunteers from all over the world, and is used by millions of people every day. Flexibility: Wikimedia is extremely accommodation and considerate. You can live wherever you want in the world, and work whatever hours suite you.
Cons
Wikimedia is a non-profit, and a lot smaller than other "big players" who run top tier websites. The base salary is quite good, but there are no bonuses or equity. Also, organizationally, Wikimedia is presently in the "uncanny valley" of professionalization: too big to know everyone personally and get things done without formal processes, but too small to have full-on professional management.