Seattle feels alive with people and is buzzing. Something as simple as the sheer size of buildings, whether skyscrapers or large in other means add to the buzz and atmosphere. The local Boeing factory and airfield means all manner of interesting planes fly very close overhead but make little noise. There's excellent public transport, excellent food (groceries and restaurants, both common and with plenty of new things,) lots of diversity among the people, wide car lanes and excellent roads, diverse choices for where to live and what type of home, good shopping, lots of economic opportunity, and lots to do and explore in and around the city.
That's what I wrote when I first landed here, and I wouldn't retract anything, but six months in and I would add that there is so much going on in the way of events and entertainment that you choose what nights to take off, knowing you're missing out on some event, or don't want to know what you're missing out on.
I'm definitely a city mouse, and this was definitely one of the many reasons why I quickly declared this permanent move to have been an excellent decision.