This appears to be a fairly new hotel, and whoever designed the rooms clearly gave things some thought -- comfortable bed, well-design bath, a variety of power outlets (US + UK in addition to the Euro kind), and good soundproofing (no idea I was in an airport). Breakfast was good, and the WiFi worked fine for me.
It took me less than 10 minutes to walk from the hotel to the United check-in desk.
The one major problem, as others have pointed out, is that the signage leading to the hotel is scandalously bad! Basically, the signs are small, and if you accidentally pass one going in the wrong direction, you might never find another one.
Here's how to find the hotel: (1) from wherever you are in the airport, find the long-distance train station (this is well-marked). (2) once you are in the long-distance train station's main hall, under no circumstances leave that hall until you've found signs for the Hilton hotels (they are adjacent, so if you find one, you'll find the other). The signs should lead you up an escalator from one of the pointier ends of the train station's main hall.