Wow! I really enjoyed my stay at Eduardo's apartment in Barrio San Isidro. There are so many positives: the price (reasonable!); the location (just south of the Manzanares River, right next to the Madrid Río Park!); the access to public transport (depending on where you want to go in the city, there is a bus stop, a metro line, and the cercanías train within walking distance!); the host (Eduardo was fantastic! He responded quickly and was easy to communicate with!); the apartment itself (very clean inside, with air conditioning, washer, television, wifi, comfortable bed and recently renovated!); the neighborhood (it's just outside the hustle and bustle of the city center so it's quiet and safe, but there are bars, restaurants, and grocery stores nearby as well!).
I would definitely stay there again. In fact, I am already planning a trip back to Madrid for next summer. Thanks Eduardo!