We stayed at this hotel for 2 nights in mid September.
As stated the hotel is easily reached by train from the airport and then a short walk from Monastiraki metro station (a map is essential though).
The hotel itself is quite nice, well located and fairly priced.
The surrounding area is very scruffy and grotty (seemingly like most of Athens) and the hotel is down some little lanes that made us slightly uncomfortable when arriving near midnight.
Sadly, my partner and I slept very very badly in this hotel. We were dissapointed to be given one of 'those rooms', adjecent to a (winding) staircase. The noise that came from people walking up and down in the early hours did not help us rest at all.
The 2nd night was worse as a Contiki group were staying, so much noise all night!
I booked the room many many months in advance of our stay though presume since I got a good rate via another website (Otel.com) this was the result!
I emailed when I made the booking to ask if it was possible to have a room with a nice view (as described on Tripadvisor), I was told this was not possible. Fair enough, but the view we did get was horrific.
That said we did not book the room strictly for the view and as others have mentioned the view from the hardly used tarrace is great.
The hotel is very well located for sightseeing. On advice from friends we visited the Acropolis site at opening, I recommend this to all as the crowds entering as we left were full tilt. We took the metro to the site to save time and arrive comfortably.
Overall I guess I would recommend this hotel for its location and convenience, just don't take a room by the stairs (especially on the lower floors - we had the 2nd floor room).
If I had my time again though I would have chosen elsewhere but you get what you pay for, as they say!

My partner and I stayed at Arion Hotel for 1 night in SEP/07. The hotel is easy to get to from Monastiraki metro staion. The reception and breakfast area are nice, mordern and clean. The breakfast itself is quite good. Our room was nice size by European standard with partial view of the Acropolis. The bathroom was big and modern. The front desk staff was helpful. The hotel is within walking distance to Plaka. We would stay here again.
Rit & Brig - Vancouver, Canada

This was a nice modern hotel. The main street facing looked not so inviting with the graffiti and abandoned buildings and abandoned church. The Adjacent street though is the place to be at night, lined with restaurants and bars it was great!! It is a 5 minute walk to the Monastiriki train station, where I took the train from the airport to. If you plan on doing the train route make sure you take a map of the hotel provided on the website with you so you don’t wander around a lost vulnerable tourist with luggage. The King bed is actually two beds put together so be forewarned, it was fine though. The bathroom was very clean and modern. We walked from the hotel to Syntagma 20 mins the flea market 5 mins, Hadrian’s Library 7 mins, Acropolis 25 minutes and very uphill walk bring water wear comfy shoes be ready to get dirty it is dusty. Hotel was very clean, the room was large and roomy and it was a great value would definitely stay there again.

Gorgeous modern hotel. The area's okay, not exactly Shangri-La, but Athens itself doesn't seem to be a looker either; makes NY looks pristine, and I'm a NY'er. There are a bunch of quite restaurants covering the sidewalks within a minute walk. A nicer more touristy neighborhood is just east of the Parthenon.