I would have rated this hotel a few points higher if not for the beds: While all the beds we slept on in Greece were firmer than we prefer and devoid of box-springs (I can understand this as we were staying in one- and two-star hotels), these beds were exceptionally uncomfortable -- another reviewer recalled feeling the springs through the mattress, and this was our experience too. Our sleep was a bit fitful, and I remember dreaming at one point that I was sleeping on a wooden plank. I think it's about time the hotel updated its mattresses; the ones it has are a bit worn out! In the meantime, I suppose the resourceful traveler could lay down the extra blankets in the wardrobe as padding to help offset the hardness of the mattress (I wish I had thought of that then).
Hotel Ionion's main attraction is its location -- it's right next to the metro station and practically across the street from the port; otherwise, it's a very basic hotel, but it has everything you need.
The rooms were clean and featured a mini-fridge, a TV with a decent selection of channels, A/C (arguably a necessity given the heat!) and a wardrobe loaded with extra blankets for wintertime tourists. The Wi-Fi signal here may have been the best out of all the places we stayed at; each floor has its own extension, so you'll likely get a strong signal even on the top floor.
The man who checked us in was neither friendly nor hostile, but when we left and returned to the hotel later, the owner had taken over manning the front counter, and he was exceptionally friendly and seemed genuinely interested in whether or not we were satisfied with our lodgings.
Overall, the hotel is a decent value for a night in Piraeus given its location and cleanliness; however, the major downside (see below) could be a caveat for those with back problems.