The Luck of the Draw
Whenever you stay in a big old hotel, and I've stayed in a lot of them, you have to understand that they probably have some great rooms, and they also have some terrible rooms. What you get is pretty much a crap shoot. Be very nice to the desk clerk, and you're more likely to get a better one. 
There are things to like about the Congress. The lobby is quite pretty. As most people point out, the location is excellent (although you might be bothered by some street noise if you're on a lower floor). There's a nice little bar just off the lobby. Because of the location, you'll probably pay more than you would for a comparable room at a hotel that is not so well situated. There's a parking garage just around the corner where you can park for about $12 a night. And they offer smoking rooms - a rarity nowadays. I asked for a smoking room, and it was qute nice.
My room and my bathroom were both quite large, and very clean. The bed was comfortable. The TV worked. I was in a corner room on the sixth floor.
There are some things I didn't like. My room did not have a refrigerator or minibar. Likewise, no microwave. There did not appear to be enough staff, and there were long lines to check in. The staff was friendly, though. I didn't make any special requests, so I don't know how they respond to those. The elevators were very slow. It was a hot day, and even with the air conditioner cranked up as far as it would go, my room was not as cool as I would have liked it. 
If you're looking for luxury, look elsewere. But if you just want some place to sleep and shower, the Congress is fine. This wouldn't be my first choice of a place to stay in downtown Chicago, but it will do in a pinch.