As a 3rd, almost 4th generation Washingtonian I'll readily admit I'm a bit biased toward the state. I like it a lot up here and don't plan on living anywhere else (though I do like traveling).
Here's a run down on the state.
The state is bisected north-to-south with the Cascade mountain range. On the western side of the state it is much milder weather with narrower temperature swings from winter to summer. It is also wetter. The eastern side of the state is in the rain shadow of the mountains and subsequently much drier.
A major inland water way, the Puget Sound, knifes down from the Canadian border and stretches almost halfway down to the OR border. This body of water connects with the ocean and helps moderate the weather in the Puget Sound region (Bellingham, Everett, Seattle, Tacoma, Olympia). It is also home to the San Juan Islands. The NW part of the state (cleaved off by Puget Sound) is known as the Olympic Peninsula with the Olympic mountains topping it off.
There are, I believe, 5 different climatic zones across the state. We have rain forests on the Olympic penninsula on the western side (150" per year, wettest place in the continental U.S., IIRC), a lowland forest area, mountainous alpine areas, high steppe, and desert regions (generally W to E across the state). And if you're in the Seattle metro area, all of these can be accessed within about a 2-3 hr drive in any given direction.
Of note, we technically have "active" volcanoes in the Cascade mountains, however, with the exception of Mt. St. Helens they have been inactive for a few thousand years. Also, the Puget Sound is criss-crossed with active geologic fault lines. Yes, this is earthquake country. It's not as active as California but it's active enough. There have been major quakes in the 40's and in 1965 which caused substantial damage to the city. The last semi-major quake was the Nisqually quake of 2001 which damage the state capitol building and knocked down several walls in the historic Pioneer Square area of Seattle as well as did major damage to Seattle's Alaskan Way Viaduct. . . and that earth quake was 60 miles away from Seattle. IIRC, I think we had a minor quake sometime in 2010. This all stems from the fact we have an induction zone off the coast of washington. The Pacific tectonic plate is diving under the Juan Defuca plate (which comprises most of the Puget Sound). As the Pacific plate melts it forces up material to create our Cascade mountain range. Lots of cool geologic history and activity in this region.
Despite Seattle's reputation for rain we actually get less rain fall than most major U.S. cities. The deal is, it's spread out throughout the year quite a bit. And there are a lot of overcast days where it may not rain at all for a week but you won't see the sun through the clouds. Some times there might be a sprinkling in the morning and that's it. Sometimes we get a deluge. Winter temperatures are usually "mild" compared to many places around the country. Lows are usually in the mid-to-upper 30's. Snow is rare in the low lands and when it does fall it doesn't stick around for long, usually gone in a day or two. Some winters we get snow, some we don't. As a result, most people don't know how to drive in the snow and the least amount shuts down the city. Well, that plus the steep hills all over the place.
If you WANT snow, the mountains are a 50 minute drive away where you can access ski resorts and snow parks for snomobiling, cross country skiing, snow shoing, and so forth.
Summers in Seattle are usually spectacular. We might get a "hot" stretch in the mid-to-upper 80's that lasts for 2-3 weeks at the height of summer but most of the time it's in the mid-to-upper 70's. So it's noticably and comfortably warm with out being annoyingly hot.
On the eastern side of the mountains things are much drier, on the arid side, really. The winters are colder and the summers are hotter, often reaching into the upper 90's and low 100's.
Humidity in the warm months is not an issue on either side of the mountains. So the high temps in eastern Washington are not bad. And there really isn't much of an bug problem, unlike other areas of the country. For that matter, I don't think there are any dangerous insect, spiders, or snakes on the western side of the state. In eastern WA you'll want to be aware that you could find rattle snakes in the drier areas, though in 34 years I've never seen one in the wild.
Most of the state's population is in the King, Pierce, and Snohomish counties (Everette to Seattle to Tacoma) and flanks both sides of I-5 from the water front to the foot of the Cascade mountains. Most of this population is pretty well educated and liberal leaning. It also has a more high-tech economic base with a number of bio-tech firms, aerospace companies (ever hear of Boeing?), lots of software and computer companies, etc. This population base also tends to swing the whole state in terms of political direction.
Outside this area the state gets a lot more rural pretty quick and much more politically conservative.
Taxes (in case you're wondering)
We have property taxes and sales taxes and that's it. No income tax. Sales tax is close to 10% (9.8% or so, I can't remember). And property taxes aren't too bad from what I understand of other states. Say it fast I think we're paying about $3500 on a ~$300k house. Somewhere in there.
Cost of Living
Housing tends to be a bit higher here and we haven't had the scary crash that other states have suffered. That said, housing prices are down now. Figure on around ~$900-1000 for apartment rentals in the area. Of course, you can go higher or lower than that depending on what and where.
As mentioned, insurance tends to be a little higher here. For the metro ares there is an emissions test that needs to be done once every 2 years. It's not bad, they're just checking emissions. If you have an OBD-II equipped car they plug in the computer to the OBD-II port, put a sniffer on the tail pipe or gas cap and you're done in about 2-3 minutes. Granted, if you pick the wrong time you might be waiting in line for a while. If you don't have an OBD-II equipped car, then you have to rev the engine as they put the sniffer up your tail pipe (on the car). Otherwise, there are no other vehicle inspections required. Licensing tabs run ~$70-ish/yr in the King, Pierce, Snohomish counties due to some mass transit taxes we've levied on ourselves. out side of this area (RTA, Regional Transit Authority) tabs are about $30/yr.
This is a major reason I love this state. We may not have the biggest or best of things, but we have a huge variety of outdoor opportunities. . . and they are very close at hand. Off the top of my head:
We have camping in all the 5 major climatic zones I mentioned above. As well as hiking and back packing. There is mountain climbing. There are winter sports which included at lest 4 semi-major ski areas plus more snow parks for snomobiling and such. Whistler is a few hours to the north in Canada and Mt. Bachelor to the south in OR is supposed to be great.
If you like the water we have the Puget Sound and the San Juan Islands for exploration. Either by ferry, float plane, boating, sailing, or go sea kyaking if you want. There are islands big and small to explore. There are also tons of lakes and the Columbia River.
There is Pacific Raceways International which is a motorsport race track for drag racing and road racing. That's near Kent, about 40 min SE of Seattle. There's also Portland International Raceways in OR about 2.5 hours south via I-5. Plus lots of autocross opportunities as well as thousands of miles of back roads to explore and drive all over the mountains.
And then there is the offroading. There are, about 9 or 10 major 4x4 jeep areas in the state. And there are more ORV areas if you include places specific to motorbikes or ATVs. Most of the Jeep'n areas are within a 1-4 hr drive of downtown Seattle with most about 1-2 hrs away. And they are in the nature of trail networks rather than individual trails. The ones on the western side of the state are very tight and twisty. They roam up an down the sides of the Cascades through lush evergreen forests with dense underbrush and get very slick when wet, which is often, especially in fall or spring. During the late spring to early fall the eastern trails are availble once the snow melts. These areas cover MUCH larger territory and you definitely feel you're out in the middle of no where. One of my favorites is Manastash Ridge which covers 115 sq miles of territory with about 90 miles of Jeep 4x4 trails (and more motorbike / ATV trails). You can go camping out there for 4-5 days and not get bored Jeep'n. And the scenery over there is stunning, especially once you get up on the ridge lines.
Wheel'n areas and travel times are:
1 hr from Seattle
Reiter Foothill Trails
1.5 hr from Seattle
Naches trail (crosses the cascade mountain rnge
N. Cle Elum trails
2 hr from Seattle
Manastash Ridge (accessible via Naches Trail)
Liberty / Table Mountain
3.5-4 hr from Seattle
Take a look below at some random photos of the Jeep'n opportunities around the state. All of these are from the list above.
Evan's Creek (winter, duh)
Manastash Ridge, a place called Funnyrocks