I arrived at 10am and could immediately go to my room and shower, before having to check-in, great service. Got a map and an excellent explanation of places to go and their opening times, very helpful. The 9th floor room was a double for which I only payed the one person fee, so I guess I was lucky. It was modern and clean with excellent airconditioning and balcony with sunset view. Wi-Fi was cheap and worked great.
The hotel is just one street away from Athenas and a few minutes walk to Monastiraki so a great start for your trips. One downside as mentioned by others: the area to the North of the hotel isn't the greatest place to be. Best avoided after dark. But since all the interesting sites are mostly south and east of the hotel, this shouldn't be a real problem for most.