Nothing can beat the location of this apartment. This was our first stay in Madrid, and we didn't know where's what until we got there and started going around. And pretty much all what you need is right there around the corner! The palace, Puerto del Sol, tourist buses. Gran Via is short walk as well as Retiro park.
The only downside is that there's quite a bit of noise coming in from the street from passing cars, although there's not too many there, but they kept waking me up as well as uncomfortable sofabed. Also the apartment is sharing the same entrace/hallway with couple of other apartments/rooms, and the residents there are absolutely inconsiderable towards their neighbours. On our last night there they kept walking in and out, slamming the doors, we barely got any sleep at all and had to leave quite early in the morning for the airport.
There was also nothing left for breakfast (although it states bed & breakfast), only some milk and coffee (no coffee machine though).
Other than that, it's a lovely apartment at a brilliant location.