The apartment itself is very clean and tidy. It isn't fancy, but everything in the kitchen and bathroom works, and the space, while limited, is organized well. One thing that might be an issue for some is that the bed is on a loft above the main living area, and that the stairs are pretty narrow and steep. There is a daybed and trundle in the living area so you wouldn't necessarily need to go up the stairs if you did not want to.
The location is the best part of this apartment. It is very convenient to Puerta del Sol, which means that it is also very close to Plaza Mayor and San Miguel Market. The area is busy and active, and has a pretty constant flow of people at all hours of the day and night. There more restaurants and bars than you could ever need in the blocks surrounding the apartment.
Overall, the value of this unit is great. Given how close it is to all the action, the overall cost compared to hotels in the same area, and the ease with which the check-in and check-out process went, I don't think you can go wrong.