I put “worth it” only because it’s one of those places you “have to go.” But, honestly, this was the least exciting of all of the things I did in Chicago. I think you get a much better overview (especially of downtown) by going to one of the lakefront parks and taking in the skyline that way. While Sears Tower is really tall and cool I would describe the overall experience as “lackluster,” since you can’t see a lot of downtown itself from the Skydeck due to its height and the fact that it is in the center of downtown.
Chicago seems to me a city better enjoyed from below, a lot of the little charms (like the amazing statues in downtown) and architectural details that make Chicago are lost on you staring down from on high.