One word - Fantastic. Everything was exactly as described on the listing.
We felt very safe and everyone in the area was so friendly and helpful. The apartment is very modern, with good internet access, dishwasher, washing machine etc.
The welcome we received from Kalliope was delightful - with fresh fruit in the fridge and a bottle of Ouzo and some goodies from the local baker to start the holiday off. Part way through the holiday Kalliope brought us some fresh eggs, figs and grapes and home-made jam and a local grape syrup that we put on our bread, which were all so good! Kalliope's apartment is perfectly located just 10 mins walk from the Acropolis Museum and the main Plaka area. It was a quiet area of town, and we did not experience any noise. The apartment was immaculately clean and a joy to stay in. Kalliope changed our bedding and towels part way through our 9 day stay. The local supermarket was less than 10 min walk away. Local baker was a 3-5 min walk away, with lots of local delicacies and good ice cream!. The people at the bakery spoke great English and were keen to help us. We had breakfast on the balcony overlooking the Parthenon which was a great start to each morning. When we got too hot being tourists, we came back for a siesta each afternoon to escape the heat of the day in the cool air conditioning. We ate twice at Lostre restaurant just 5 mins walk from the apartment - delightful gem, much better than the touristy places in Plaka. There is parking below the apartment - which was great for parking our rental car which we hired to explore outside Athens.
In summary - you really could not find a better place as a base to explore Athens.