Pros
Obviously, the best thing about working here is the people. The executive management really knows what they're doing, are very transparent, and do a really good job of making sure this is a place where people want to come to work. There's a reason they're consistently named one of the best places to work in Seattle.
The hours are very reasonable, and the management does a good job making sure developers aren't over-worked. The team sizes are small enough that you get to play a critical role in the development and decision-making of the projects you work on. Also, as a developer you get to learn every part of the development cycle. There's no front-end/back-end/ops, every developer is responsible for each role, which was the main draw for me, as I wanted to learn more than just the back-end work I was siloed into at my previous company.
They pay was also reasonable, but by far the main draw of working here for me was the laid-back work environment and ability to work on all aspects of a product.
Cons
Being a development firm, you will obviously get client work that could be considered "less than exciting", from time to time, but as the company grows they will get more interesting and high-profile work.