Our stay at the Keti Hotel was one of the highlights of our Greece holiday. We would happily go back.
Yes, you have to go up or down some wide stairs, but this was easily even with luggage as long as you can walk normally. The advantage is that you have a wide patio with tables to yourself to watch the sunset, to eat the freshly made breakfast (lots of options, very tasty) or to have a quiet glass of wine watching the sea away from the crowds that were elsewhere in Santorini.
The rooms were clean and the beds comfortable. Internet worked well, too, which was appreciated.
The hotel is a very short walk (3 - 10 minutes) from lots of bars, stores and restaurants in town and was very peaceful at night because of its location.
The manager and staff were very helpful during our stay with good restaurant suggestions (we had many tasty meals, from simple to fancy, following their suggestions).