The Athens restaurant world has changed considerably over the last 10 years or so (amazingly, during the big financial/economic crisis of the country). You can nowadays find several "starred" restaurants with very good to excellent cuisine, the only problem though (in addition to their high prices) for me is that most of them don't serve "genuine" greek cuisine. There still , though, are several good tavernas throughout the city that are worth a visit. Most of those are in residential neigbourhoods away from the touristy and business areas (e.g. Pagrati, Kypseli, Petralona, etc. as well as in Piraeus, and many suburbs). If one likes some adventure, I'd recommend walking or taking the yellow trolley bus to Pagrati, get off at Plastira square, then walk around the area above the old Olympic Stadium and pick any of the many restaurants that look busy (usually tables on the sidewalk) and the people look... Greek. The chances that you'll be satisfied are very high