Pros
High-priority and high-visibility work that has a direct impact on paying customers. Great to see how my day-to-day directly translates into what a user sees within their account. Increasing levels of responsibility and project importance once you prove yourself. Large paying customers in a short period of time is a great sign. Long-term vision for company and the moonshot goal is something you can definitely get excited about. Not always the case at every startup. Easy access to founders. Openness and transparency on everything a huge plus - having open Q&A with founders during company-wide meetings. Very generous 401K and match.
Cons
Juggling multiple hard deadlines can sometimes feel like a lot, not for those that want to always work 9-5 and check out after work completely. Accounting and the terminology can be confusing at the start. Not a ton of snack/drink choices.