The apartment is nice furnished and was also clean. There is a nespresso machine in the kitchen, which was a nice surprise. Also the apartment is extremely central, so that you practically don't need the metro as you can reach everything by foot. The only thing bad about that is that it gets loud at Night, but with a pair of earplugs it's no longer a problem.
Israel, the Host, was very welcomming and helping with everything. He also offered us a Space, where we could keep our bags, the last day, because the flight was at night and we could enjoy the city without suitcases.
All in all, madrid is a great city which you can enjoy a bit more in this apartment :-)