Pros: modern design, spartan but comfortable furnishings. Walk-in shower, only moderate water pressure. Great air-conditioning. Very good blackout curtains (we were with our 3 and 1 year-old kids who nap). Pool was warm, jacuzzi was not yet hot (just opened for season). Breakfast buffet was full of options (yes, an omelet station!) and coffee is very good. Wireless internet is free, and has great signal (we were in room 413). For dinner, choices were classic american fare at budget prices, with a very friendly server/bartender (don't remember her name). Some micro-brew beers were available. We could see the arriving planes on approach out of our double-glazed windows, but could not hear them. Don't know if departures would be audible.
Cons: We booked through American Express, which was our mistake. They put our reservation in for wrong nights! At the front desk, Betty was very, very helpful in accommodating and rearranging our reservation. Better to book directly with Hyatt or through online service, not with a human (fallible) agent on phone at American Express.
We found crumbs in sofa bed mattress. That mattress had no sheets on it. Anna, also at front desk, quickly arranged for housekeeping to clean crumbs and get sheets. She was surprised the bed had no sheets on it. Housekeeping didn't really get the job done for a couple of hours. Juana (housekeeper) finally came and cleaned.
Overall: Staff was super-friendly and helpful. Hotel was crisp, modern, budget but elegant. Location, well, it's near Dulles Airport, but absolutely nothing else. There isn't anything withing walking distance.
We paid around $100/night for the one-bedroom king (french doors close the bedroom off the main room). Great value!