This is a great way to see Chicago especially if it's your first time, and if that's the case, do this on your first day so you can get an idea of the lay of the land and which things you'd like to spend more time with. It's great to be able to "hop on and hop-off," but be sure to watch your time since the buses only run every half hour, you don't want to just miss one.
Different drivers give different information, some are more informative than others, but be sure to grab the earphones to get the most information. You should also check to see if the buses will be running the whole schedule, they ended earlier than normal on our day.
Overall, I would recommend this tour.