We stayed at the Eridanus for one night on our way back from the Greek Islands. We checked in fairly late around 8 PM and were upgraded to a junior suite :-) which I must say was the best room I've ever got in a hotel anywhere especially since we paid only 150$ for the room. Ok.. I know this review will not decribe a typical room since we stayed in the junior suite but I can write about the suite: to say the least, it was perfect. The flat screen TV, marble bathroom with full body jet shower, Hermes bath products, digital room control was excellent. We paid 10$ for all day internet service so we could check email etc. and its a great deal ; it also comes with wireless keyboard so you can lay in bed and check your email, pay bills etc etc.
For dinner we went upstairs to the french restaurant on the roof top patio. A little expensive but the food was excellent !!! I am normally leery of french restaurants because in my book they charge a lot for not enough food (and we were starving) but we were stuffed by the time we left. The food was fanstastic to the point I had to make a comment that the food was better than the view (and the view was great - view of the Acropolis lit up at night).
Service was outstanding. I would give the french restaurant 1000 stars if I could. A little expensive though, we spent around 110 dollars but I think thats actually cheap because its ranked number 2 in Athens for french cuisine ! Also seems that the customers dining there are very upper class counting the number of chauffered mercedes limousines that were waiting infront of the hotel; however, given that we didnt have chauffered mercedes, or werent wearing rolex or luis vuitton, they still treated us extremely well.
Breakfast in the morning was also 1000 stars !!! they had the best possible products on the buffet - salmon, fresh orange juice, hot and cold breakfast item etc. We ate like pigs (not because we were that hungry but damn the food looked really good). we actually ate so much that we didnt eat the rest of the day !!!
Also the furnishings in the hotel are very nice. Its entirely in marble with numerous art pieces in the room as well as hotel.
we checked out at noon and left our bags at the counter so we could check out the city. They did not charge for this service and even labelled our bags.
The location of the hotel is excellent. Its right by an ancient church and cemetery. You can pass by the cemetery and buy tickets that will also cover entry to the acropolis. Its also about 3 - 5 mins walk from Thirassia train station where you can but a 2 euro 24 hr rail pass. Its about a 15 - 20 min walk to the acropolis or you can take the trainb to monstraki (next stop from thirassia) and walk there in 10 mins.
Staff at the hotel were more than excellent. Very professional and courteous.

So... it was primarily upsides in my review. We are not budget travellers (we spend around 150 - 200 $ a night for hotels when we vacation); the only downside I would say is that its not in a very posh neighborhood. If you are more of the glitz and glamour crowd used to staying in hotels with big huge foyers in country club locations, then you might not like the location. If you are more of the adventorous types who like to combine luxury with a little bit of walking, taking the bus/subway then this hotel will definitely be an A++ for you.