Pros
Fun group of people (Jeopardy on Fridays) who enjoy working together.
Basically unlimited opportunity to learn new things, come up with new ideas and take ownership of and run with them. Senior people/founders not only listen but encourage and actively solicit feedback. They are interested in employee growth.
Energy and passion of leadership for what they do is obvious. Company has a clear niche, direction, and purpose that drive pretty much everything.
Product is easy to get behind because it offers clear value, no gimmicks.
Cons
Nothing other than typical startup/small company stuff.