Pros
I've made some of my best friends here. Everyone is capable and comes from different backgrounds, and there's a culture of people helping each other. I've always found it easy to ask others for help; almost everyone was ready to make time to answer questions or give advice about something at work.
Cons
The usual problems with fast-growing startups: there are some organizational growing pains as the company scales. I feel Stripe handles this very conscientiously, though - there are concerted efforts to make sure teams are working well together and reduce the friction that occurs when it's harder to know the entire company. There's slight imposter syndrome here - because everyone else is so talented and helpful, it's possible to feel that everyone else is way more capable than you. But hires are made very carefully, so a bit of self-confidence will be useful here. There's also a lot going on, and most roles here have to serve as interface to many different parts of the company, so at times it can feel like there's a lot to juggle.