Pros
The people are awesome, very supportive, and really welcoming. The projects are very interesting and people who do well are given more responsibility and opportunity to take on more interesting projects. People who are doing a great job get recognized and rewarded. The flat structure means that everyone is in contact with the executive team and they can ask questions or get feedback without going through many levels of managers. There is a flexible work schedule, meaning that people can take time off when they need it or work from home without any prior approvals. The company perks are great too - Friday lunches, snacks, ski trips and tickets completely paid for by the company. When employees are struggling in their roles there is a heavy focus on helping them improve before any changes are made to the team.
I've never worked anywhere else where the people were so consistently fun and highly skilled.
Cons
The company is growing very quickly, and because of the focus on hiring both for skills and culture fit, it can take a while to find the right people. This means that some teams are understaffed. However, Management is very understanding of this and the company is actively recruiting for these roles.
Expectations on performance are high, and that means that some hires don't work out, or the company just simply isn't right for everyone. I don't really see this as a con, however.