Sharpest of the Club Quarter hotels I've stayed in
The Central Loop CQ is the cleanest, most polished and well-serviced of the CQ I've visited: NYC (all of the hotels), DC and Chicago. The best word I can find is "sharp." The feeling you get is that the people here care about the place, take pride in it, and want to provide you with the very best experience possible. The sitting room off the lobby is quite comfortable and the "living room" downstairs is about the best club room I've seen in this chain.
Yes, the rooms are small. But you don't go to Chicago (or NYC or DC) to sit in a hotel room. You're there to sleep and shower. Maybe work a bit. And the Central Loop CQ's club rooms seem to be a bit more spacious than those in the other hotels. 
The staff is pleasant and helpful. (I had a problem with the valet staff, but it was handled quickly and resolved to my satisfaction.)
The location cannot be beat. You are steps from most of what the Loop has to offer or within a block or two of access to the El for more distant destinations. 
We were in Chicago for a wedding and MOST of the guests invaded the hotel for the weekend. I really expected some kind of slowdown or hiccups with the service, but I experienced nothing but first-class service.
So why not FIVE stars? I had problems with the online reservation system. I originally reserved rooms over the phone. When I discovered that we wouldn't need to come into Chicago as early as I had expected, I went online and modified the reservations. WARNING: do NOT trust the online system to process your request. My changes were NOT processed and I paid the cancellation penalty. I was a bit nervous the night before we left, so I called CQ to confirm the modification in our reservations. Wendy, the CQ rep I spoke, couldn't find the changes but she helped me greatly in guaranteeing the balance of our reservation -- I did not want the rooms cancelled on us -- and she called the hotel itself to make doubly sure we were in good shape. She admitted to me, however, that the online reservation system isn't reliable. So take that as a warning. Always call, always ask for a NEW confirmation number, and always note the date/time of the call and the name of the rep who helps you.