Now that I've stayed at the Park Hyatt about five times, I think it's time for a review. This hotel is consistently one of my favorites and is by far my favorite hotel in DC. I've tried the Willard, a couple of Ritz properties, and many other upscale chains. Nothing comes close to the Park Hyatt. It is unpretentious, modern, trendy (but not super hip like W Hotels try to be), and caters well to all ages. The staff is amazing, super-friendly, helpful, and professional. Even the smell is inviting. I think they pump some mild scent through the hotel.
The onsite restaurant, Blue Duck, is one of the best restaurants in the city. Make your reservations early. It is NOT your typical hotel restaurant. It would be a champion as an independent site in any city in the world. Be sure to try it. In the lounge are a small bar and the Tea Cellar, offering dozens of luxury teas, and kindly, free refills of water for multiple steeps. Compared to the $18 gin and tonic I had at the bar, the Tea Cellar seems like a bargain.
The rooms are larger than other upscale hotel rooms in DC and the bathrooms are beautiful. I also think the rooms have character with a split living room/bedroom concept and a modern style. Some on here have commented that the colors are bland, but I find the rooms peaceful. I like the unusual but perfectly adequate lighting, the colors, and the amenities. One important tip that will make the stay better: the super cool bathroom of the Premier Park Deluxe room (or better) is well worth the extra money. The large open marble shower/bath concept is awesome. I could stay in there all day.
There are only two negative things I can think of to write. First, prices for everything are ridiculous - even more ridiculous than most upscale hotels. Valet parking is $48 per night for example. That's unconscionable enough that I specifically don't use it and taxi to/from. Maybe that's what they're going for. Second: no spa. They have a "spa room" but that it is just a normal hotel room retrofitted with a massage table and some other spa items, but it is NOT a spa. Furthermore, massage prices in the lackluster spa room are, like everything there, stupid expensive. $175 for a 65 minute Swedish massage is the cheapest option. Maybe I'd pay that if it were a real serious spa and I could spend some quality time relaxing before and after.
As long as you know going into the stay that all of the hotel's services are very expensive, don't hesitate to book here if you can afford the room. I wouldn't stay anywhere else.