Nothing outstanding
Affinia Chicago is a good hotel, in line with most 4 star and above hotels in and around the area. I didn't really see a definitive aspect of the hotel which made me think i would always stay there when i visited Chicago, though.
As far as location goes, there are other hotels in the same area around the Magnificent Mile so i don't think that's really a competitive advantage. The staff were friendly, but a couple of times when I called the front desk, i heard them making jokes and they seemed a bit stand distracted. Nothing major, overall they were friendly.
The room was good, a bit too large for a single bed room but it was quite nice. Sleep quality was great , not too impressed with in room dining for breakfast. 
In my opinion, they should provide free WiFi to guests. The base rate of the hotel is not exactly cheap, so that is one aspect where they can improve. The TV in the room was not working on some channels, fuzzy on others. One of the telephone sets didn't work.
I didn't stay in the room all the time, so i didn't raise these above issues with front desk on this trip. 
Overall, a pleasant experience but i think it missed some of the personal touch that would make me feel right at home and ensure i always stayed with them on visits to the windy city.