Living the car-free life in Seattle is depressing due to gloomy weather. Life in Seattle is great if you accept the grey and live outdoors as much as possible. For that you need a car.
Sure, if you want to go out to the mountains every weekend you need a car, but with a light rain-proof jacket, it's not too bad to walk or bike through much of the city. The grey weather is either depressing or not, but I don't find it to be much more depressing out of a car than in it.