We stayed in a rather grand suite, with twin beds and a large lounge, in late November 2011. The hotel consisted of 2 (or maybe 3) buildings next door to each other in a small plaza off the main road. Too far to walk to most attractions for most people, I would think, but it is easily accessed by metro if you use the southern most exit from the Rios Rosas line (I think it's line 1 but check). The exit is for "Plaza del Descubidor Diego de Ordas" and is right opposite the plaza and the hotel reception is in the second building on the left, about 100 meteres from the metro exit. The continental style breakfast was in probably the best of that type we have had anywhere though we had to go to the building next door for it.
We had a discount price of around £65 inc breakfast and for this it was excellent value but even at the full rate, which I think would be around two and a half times as much, it would be acceptable value (though we couldn't afford it!)

Stayed for three nights. Have mixed reactions that results in an overall average rating. On the plus side: the suites provide an unusually large amount of room for a European hotel, the metro is steps away, the breakfast is top-notch with very friendly assistants constantly re-stocking and cleaning. On the downside: the location is in a not so interesting part of Madrid (but easily reached via the metro), friendly enough day front desk staff but rather rude individuals in the evening, noise - all kinds of noise - the noise came from everywhere, including the footsteps of what seemed like a 300 pound gorilla in heels in the room above me, fire trucks, shaking walls, etc, expensive in-room internet service that consistently dropped out.

I spent 5 days in NH prisma in October and would come back again. Suites are very well fitted and comfortable. Staff was friendly and discreet. Hotel is next to metro station and it takes only 5 station (10 mins) to reach city center. Although there is free wifi at the reception area, there is no free internet in the suites and the cost of having one is rather expensive @ 10 eur/ day. Also, you can't get dinner at the hotel, however hotel offers good deal for in room deliveries of pizza's and burgers.

The reception staff was not very friendly (cool and distant), overall the hotel itself was very conveniently located, right across from the Rios Rosas metro station which is only a few stops from central Madrid.
The breakfast buffet offered a wide choice of breads, juices, meats, cheeses, fruit and even chocolate doughnuts! There was plenty of choice and the stock levels were always kept up so no problems there. The breakfast staff were friendly.
The worst thing was our bedroom (1st level) with views to the opposite building (congested boulevard or a cement courtyard) from wich we could listen and feel the sounds from metro passage.
Internet (expensive and not private) was availble in the small lobby space.
Would recommend the hotel just for those who have deep sleep or stay on a higher floor.