Lot of good things but poor lower management is a huge pitfall
Pros
It's quite a lot of stuff, I'll have to list them: international fun people, perks in the form of parties and drinks, flat hierarchy, challenging fast-paced environment with opportunities to grow and learn, freedom to take on projects and responsibilities. I have also always genuinely admired the athmosphere in which speaking up is encouraged a lot. I felt to be part of something really big, while keeping the startup vibe. The culture totally sucks you in, in a good way, very energetic. Had a lot of fun, learned a lot, and the experience was totally worth it.
Cons
Managers. Due to huge growth the company started hiring and promoting the wrong people. Low and middle managers are underqualified and are not just overstretched but they simply don't even necessarily understand what's expected of them. You can actually witness people fleeing away from teams with incompetent team leads who would either cause significant impairment in the fuctioning of the team or weren't able to solve any of the existing problems. Speaking up to the relevant higher level managers unfortunately does very little, as they are overloaded with too many teams, thus they end up having little or no time to solve actual issues. So you're pretty much stuck. Additionally, some product managers have been losing focus, and instead of trying to help the user, they are making up projects that they 'think' is great - it's very demotivating to work on ideas you don't believe in. Also, they have weird and not transparent ways of dealing with long term mental illnesses and burnouts. Pay is not super generous either.