TL;DR
Central location, clean apartment; Highly recommended.
Long Review
Just got back from a short trip to Athens. 3 adults, we stayed at Nik's. The communication with Nik and his wife was excellent. Nik could not stay to greet us upon arrival because our flight was delayed. We were greeted by the cleaning lady, who was very friendly, and spoke on the phone with Stella, who welcomed us heartily.
The apartment, which was exceptionally clean, is located in the heart of Athens. Everything is within walking distance. Acropolis, shopping streets, coffee shops, markets, metro. I would describe the neighbourhood as lively. Our bedrooms were located in the backside and the noise from the bars across the street was not noticeable. Although I had brought ear plugs along, there was no need to use them. The bedrooms were quite and we could enjoy a good night's sleep.
Nik's hospitality exceeded our expectations and I cannot praise him enough. Next time I visit Athens, Nik's apartment will be my top choice.