It's one of those experiences, that everyone should try at least once, if they can. The upper level is indeed quiet and relaxing, with those big window views on the street, but I find the lower level to be equally relaxing depending on mood. I like the tall backed chairs on the lower level, and you're also closer to the service station with water, tea/coffee, and occasional snack offerings. No idea what this looks like in the pandemic area, hoping to find out this Spring.
The key is to find a spot where you can be comfortable waiting for a short time... or longer. Sometimes it's great just to stow your bag and explore Chicago until boarding time.