So I am a biased reviewer, so instead of writing one, I grabbed one from the Go Seattle Card site (although extremely positive, he does provide some useful tips):
I absolutely love this card! I was in Seattle for work and decided to take in a few sites over the weekend. I did the winery tour, which could not have been better, and had a blast. Everything except food and my gifts was included. I did so many things that I would not have done if I had to pay the admission price, like the music experience, science fiction museum, mono rail, and the lake cruise.
The one thing I would highly recommend is to get the card as soon as possible. I waited until mid day on Saturday and lost valuable sight seeing time. I would also really think about all the things you could do with the card and how many days you need it for. I bought the 2 day, but once I started using it I wished I had bought the 3 day for the extra $10.
Everything you get with the card is first class! Don't be afraid that you will have second rate seats or options. It is so worth the money!

Seattle has been one of the best cities in the states...that's my opion. It is close to the beach and not far from the mountians. There is so much to do in the city and just as much on the outskirts of it. Plus it's the coffee capital of the world. Doesn't get better. The Go seattle card is a big way to save cash if you plan on touring.

Lived in Seattle for 3 years; visited several times - it is one of the great cities....love being surrounded by so much water and trees. Terrific B&B's. Best time to visit -- September.

Visit Pike's Market and the floating houses on the Puget Sound (Sleepless in Seattle). The EMP (Experience Music Project) Museum is great!!!

great place to go to city is nice and a 45 min drive you can be in the Parks Hiking