We stayed at the ACSH for seven days.
Our stay can be described with one word: EXECELLENT
The staff were very welcoming and helpful - recommened us places to go eat and when to take the metro,. We had a room facing the market in front of the hotel, but we didn't notice any noise in the morning. Room was neat and clean (eventhough our room didn't face Acropolis, we had an amazing view over Lycabettus Hill). Morning buffet was as expected - usual stuff (eggs, bacon, juice, bread etc.)
The rooftop view was simply amazing - couldn't imagine a better view. The rooftop had a bar which opened 6:00-6:30 PM - like the rest of the hotel, great service here as well.
Would we recommend this hotel? Yeah, if you're looking for a hotel centrally located and a helpful staff, this is certainly the place to be!