Pros
Energetic office filled with people who believe in the mission of the company and want to see it succeed. We got to solve new and interesting problems in an entrepreneurial way. I also received good equity-based compensation on top of a competitive salary.
Cons
I was at the company during some startup growing pains. People were being challenged to accept new roles and responsibilities that they weren't always ready for. The company was good about support (especially if you seek it out from some of the managers who have been there for a while) but some employees were unhappy about the constantly expanding responsibilities. I understand that things are becoming more stable, but any growth startup will always challenge people to grow; I personally enjoyed being to expand my career and try new things.