I've never been to Seattle, but as a Chicagoan I feel I have to step up for my city.
Chicago is a worldclass city because of all the great neighborhoods and tons of things to do in them. I don't know if Seattle can compare, it only has 3.7 million in the metropolitan area while Chicago has 9.5 million. Lakeview, Wrigleyville, Lincoln Park, Wicker Park, all great places to hang out with a good scene for partying, shopping. We've got a great restaurant scene, one I'm sure is betters than Seattle's. There are nice cultural opportunities here because we have 2 worldclass universities (Northwestern, U Chicago) and a good set of museums and good theater.
It matters what you like, if your idea of a good time is just hanging out at home, then you could probably live in Smalltown USA. Seattle isn't a huge downgrade from Chicago and I'm sure Seattle would be a great place to live. I hear the pacific northwest is nice, mountains beat corn.
If money is what matters then Seattle should be cheaper. Check out CNN cost of living calculator. Normally I'd push harder for Chicago, but I don't think it's that much of a downgrade to move there. One thing I like about Chicago is by living here I don't need a car, saves me a lot of money.