Good three star, not four star, star hotel in excellent location.
We booked on Priceline (name your own price for a four-star hotel) for a quick weekend away in Chicago. We wanted to be downtown near everything. 
The "four star/four diamond" Hyatt Regency was fine, but it wasn't a four-star hotel in league with other four star hotels in Chicago (the Sofitel, the W, the Palmer House, etc). This was a solid three star business hotel, in an excellent location, but definitely not worth the four star price. 
There were good points to be sure: helpful, efficient staff, smoothly managing an overwhelmingly large hotel. The rooms were adequate, though nothing special, and the location, right on the eastern end of Wacker Drive, couldn't be beat for doing a day on foot around the Loop and Magnificent Mile. 
Also appreciated: when we checked in early, the woman at the desk said they did have a room open, but cautioned us that it shared a wall with the elevator, and could be a bit noisy, then gave us the option to wait for another room to open. I really appreciated the heads up on the situation and the fact she gave us the option. When we got our room later, it was far from the elevator and very quiet.
However, it was the little things that make a four star hotel a four star hotel that were missing from the Hyatt. When we got in bed at night, we realized that there were no fitted sheets on the bed, just flat sheets tucked under, creating that annoying situation of the sheets coming lose in the middle of the night. The toilet paper in the bathroom was really low quality, the kind you'd find in a public restroom. The shower wasn't fantastic, the water pressure wasn't great. These things don't make a hotel a bad hotel, but these are the little details that separate a four star hotel from the pack. 
That's the thing with the Hyatt Regency. There's not anything wrong with it, but there was nothing that made it stand out against three star Marriotts or Doubletrees. It was adequate, but not special or four-star in any way. 
Also, the reports of $52 parking are true (we came in from the airport via train though), however, you can't hold it against the Hyatt, as when walking around the Loop area, pretty much every decent hotel had a sign for $52-per-day parking out front. So if you're staying at any hotel in Chicago, be it the Hyatt or the W or the Swissotel, plan to spend $52 a night on parking. Don't blame the hotel, that seems to be a Chicago going rate. 
The stay was fine, but in terms of value-for-price, we likely wouldn't stay here again.