Just completed a one-night stay here over New Year's Eve. Booked a My Elite Rate for $71 several months ago and applied a DSU as I wanted NYE to be a bit special.
Location: very close to the Rosslyn metro stop, although the entrance to the hotel from the Metro is hard to locate (right on the corner, you enter through the parking garage and then have to take the parking elevator to the lobby). If one didn't know where they were going, it would be easy to miss and the walk would increase from one block to two. There are several restaurants within walking distance; we ate at the Pho 75 up the street (maybe 4 blocks away from the Hyatt) and it was cheap, tasty Pho. There are also several options for groceries/supplies very close: a Safeway about a block away, a CVS about two blocks, and a 7-11 about three blocks.
Check-in was pleasant, recognized for my Diamond status, provided with two breakfast coupons for the restaurant (Cityhouse). Was slightly disappointed there was no lounge here, but I did know that going in. There are not very many suites in this property, apparently. We were booked into an Executive Suite which was a standard Hyatt suite with living room/sitting area and separate King bedroom. The bathroom setup was a bit odd with both a shower/tub combo and a walk-in glass shower, with the toilet between them. Two sets of amenities for the two showers.
Everything was standard Hyatt, so I'm a bit baffled by the low reviews online for this property as well as some of the comments upthread here. I experienced nothing that wasn't up to usual Hyatt standards.
Breakfast was pretty decent, with a nice buffet spread at Cityhouse. A few things there I've never seen before (several jars of various toppings like seeds and fruit for yogurt/oatmeal). The service was excellent.
I think I'm pretty sold on this hotel when visiting DC. It's really close to the Rosslyn metro stop; one of the things I don't like about the HR Capitol Hill is how far away it is from Union Station or Judiciary Square, and then you're still stuck on the Red line. Rosslyn is much more convenient as three lines (Blue, Orange, Silver) run through there all the time. The only upside to the Capitol Hill is the lounge (although I've never experienced it as I was a lowly Platinum when I stayed there).
Overall, I definitely recommend the Hyatt Arlington. Do not be scared off by the Virginia location or the low rates; this is a perfectly serviceable Hyatt property in the DC area.