Location wise you can't beat it, close to the big galleries, surrounded by bars and restaurants, and not too far away from the heart of the city. There's a metro a couple of blocks away, which with a couple of changes gets you to and from the airport.
The décor is great, as can be seen in all the photos and the bed was lovely and comfortable. However, I think only two rooms have a view of the street, so make sure you can get those if possible.
Then there's the stairs, we were prepared, but they're still a tough climb after a a day exploring Madrid!
Finally, it's no longer a B&B, if you want breakfast you buy a voucher from the staff and go off to one of a couple of cafe's for your breakfast. We found we were better off to just go and find our own breakfast, there's no shortage of places nearby and many were cheaper than the voucher.