Pros
Awesome, relaxed workplace with highly intelligent people. You get to work with small teams on interesting projects with a variety of clients, where developer input to product design is taken seriously, and you can go home after a 40 hour week. Expect to take initiative and be challenged to develop your skill set. Very Agile-focused development process, with an emphasis on TDD and fast turnaround of stories/projects. A great place to work if you want to take pride in your job and have a life outside of it. They go out of their way to identify talented, promising people, often from non-conventional backgrounds, over cookie-cutter CS graduates. About as un-Silicon Valley as you can get, I hope the culture here becomes the norm for Seattle!
Cons
You get paid a decent salary, but not stock options, so if you're looking to cash out a billionaire at 35 this place is not for you. Also not for you if you just want to be buried in the bowels of a 200-person team. There's not much of a ladder to climb, you'll have to prove yourself to the world on the virtues of your work not on your ability to play politics.