We stayed for a weekend in Antonis's place, and enjoyed it a lot. The apartment has 3 floors: entrance with a living room and a kitchen (and a small veranda); a second floor with a bedroom and a shower; and - through another veranda - there is access to a private roof. The verandas and roof are just amazing - with great view of the Acropolis and area around it. The apartment was clean and tidy, and the kitchen had everything we needed. The apartment is located very close to Monastriaki pl. and Ermou street - which I think is be the best area to stay in, as it has many stores, bars, cafes etc.
One thing to note though - this area is not quiet, with all the night life going around, and the bedroom is not soundproof. So if you're sensitive to noise, do bring a pair of earplugs.
Antonis was helpful and friendly, and helped us with both somewhat earlier check in, and a late checkout, which was highly appreciated.