Pros
The people are fun and work hard, your colleagues are motivated. You will learn a lot and interact with many different teams. Benefits are solid. The good managers are great. Open and accepting hiring practices. If you work hard and make sure you get noticed by the CEO, there is room for advancement.
Kontras
Work-life balance is poor. Fires (metaphorical) come up often and they consume much of your time. Management can be unrealistic about how long certain tasks take. Turnover is very high, documentation low. Pay is lackluster. Business is run like it is still in a garage. Enterprise tools shunned in favor of cheap alternatives. Product stability is put secondary to new features, often based on CEO's favorite customers, not necessarily most requested.