This review is based on receiving a very nice upgrade the day we arrived from a basic ensuite room to the penthouse apartment (I did say very nice), so obviously my evaluation is a touch biased. However, I will say that the penthouse apartment was outstanding, extremely clean, with lots of modern touches (ultra-trendy bathroom, full kitchen, king bed, and enormous). The place is basically a hostel, so there are a lot of younger people (we are in our mid-twenties) so it this allows for a couple of extras including a "free" guided tour of the city (tips are requested and deserved) and a pub crawl.
Another great bonus is the 7 euro breakfast which was excellent. Far from the "croissant and a coffee" affair, this breakfast includes made-while-you-wait omelettes, pancakes, bacon, sausage as well as a wide assortment of fruit served in a very cozy basement lounge. Another nice benefit is that the reception desk has public transit tickets for sale. Add reliable wifi service and 24 hr door staff, and for the price of a solid pension you get a top-notch stay.
The only "negative" is that it is a 15 min walk from the old town. This was not a major problem for us, but some might prefer to be closer. However, for trips to Prague Castle, the hotel is right next to the #22 tram which takes you straight there.