Just returned from the Sheraton Seattle yesterday. They opened the new tower and the new lobby on Friday. Still some construction to deal with but its not too bad. The new restaurant opened on Monday.

I definitely wouldn't rent a car at the airport. There's a Hertz one block from the Sheraton that has evening drop off and the rates are pretty good. It's probably cheaper to rent the car for the day and return it then to pay for parking at the Sheraton.