This hotel was truly exceptional. They upgraded us to a better room for free (and we got to compare, because they accidentally took us to the smaller room first). It was very clean and they even brought us some welcome Greek snacks. The only blemish was that the floors are a light wood that is heavily scored by what I assume are luggage tracks, but this did not significantly detract from our stay.
The service at reception was excellent the first day, and the receptionist provided us with all the information we needed to quickly orient ourselves in Athens. He was there for the first 24 hours; his replacement was not as good, but still very helpful.
The room was very comfortable and very large by European standards. The location is very good for walking to the Acropolis, and it is about a 10-15 minute walk from Syntagma Square, which is about as good as you can get in Athens. If you use the metro from the airport (which I would recommend as long as there are no strikes and you keep a close eye on your things—pickpockets are rife on the metro), you can get off at Monastiraki Square, which is a 3 minute walk from the hotel, and you don't even need to change lines. The neighborhood is a little run down, but I honestly think that has more to do with the state of Greece's economy than with the neighborhood. You will find that literally everything in Athens is now covered in a lovely, thick layer of graffiti.
Everything else was excellent. The breakfast was simply amazing and included in the price. We really enjoyed it, and they even encouraged us to get more than we asked for. The only blemish is that five minutes before the taxi they called for us was supposed to show, another taxi driver stopped on the street and went in and tried to negotiate with the front desk to carry us, and they told us to go with him! Fortunately, he turned out to be very nice and honest, which is not the case with every taxi driver in Athens, but I think we got lucky and the hotel staff should be more careful about who they hand guests over to. The whole point of arranging a taxi in advance was so the hotel could get someone that they trust to carry us very early in the morning to the airport, and it is not normal for a taxi driver to walk into the hotel to ask the front desk to take you before the scheduled time for the original taxi has arrived.