The apartment is in a great location in the centre of Madrid. We used the metro from the airport and although you do have to change twice it's quite straight forward and took about 45 minutes. The apartment is less than 10 minutes walk from Sol station. The street is quiet despite being so close to the centre so we weren't disturbed by any street noise.
The apartment was great - perfect for three of us but plenty of room for four. The kitchen had everything we needed to cook on the couple of nights we decided to stay in and the supermarket just around the corner is a good size with plenty of choice.
The apartment is within walking distance of all the major sites - Prado and other galleries, the palace and the cathedral. There are plenty of places to eat out and the Mercado de San Miguel is definitely worth a visit and again within walking distance of the apartment.