It has the highest cost of living to average wage ratio in the nation.
What that means is that the average person pays more and makes less in Seattle than anywhere else in the country. Of course, if you happen to be in a field that turns out a substantial salary that might not be an issue (bear in mind that "average wage" includes all of our jobless hippies who throw the curve).
Gun laws are pretty friendly. The lack of class III has been mentioned. Beyond that the state resembles some of the best as far as unrestricted firearms ownership/carry. There is a very short list of places that are off limits, and there is no "signing provision" that makes it a crime to carry anywhere else (I.E> a "no guns" sign just means that the owner doesnt want you to carry, you arent commiting a crime if you do). On the other hand i can count the amount of convenient ranges on one hand.
If you have kids that you care about at all you DO NOT want them to go to a Seattle Public School, period. I cannot stress this enough. There are decent schools outside the city limits, and of course, the private schools are excellent.
Traffic is getting to be an increasingly significant issue. Your pretty much between a rock and a hard place if you are looking to work in the city. You face either massively overpriced homes, or absurd commutes with little to no public transportation available.
Washington is a great state if you live more than 20 miles away from Seattle. Any closer than that and you get stupid taxes, stupid lawmakers, and stupid people, all in more abundance than you could imagine.