This is great value for money but you need to be very organised otherwise won't get too much of it. They offer access to most of the attractions in Chicago (and skip the line in some cases) but you can only do some of them in the given time. It is important to know that the card is only valid until 5:30 pm which means that even though the attraction is open you will not be granted access after this hour. I had to pay for the Ferris wheel because because I didn't pay attention to this detail. Also, some of the boat tours are seasonal and conditional on weather, so check in advance. The Architecture river cruise is a must do and hands-off the best experience I've had in Chicago.
I liked all the activities we participated in...The Art Institute, the Shedd Aquarium, the Field Museum, both towers and all three boat rides. We also did the hop on hop off bus ride but we didn't feel it was as good as the red hop on hop off busses we have ridden in the past. The blue busses included in Go Chicago took forever at every stop and the tour guides weren't as good and were very hard to understand. However, we felt that the Go Chicago card saved us a lot of money, was easy to use, and was worth it. :)
I would recommend getting the Go Chicago Card because it allows you to really tour the city at your leisure and to be able to get great discounts along the way. Go Chicago!