I found our stay at the Yiannaki Hotel to be pleasant. The grounds are excellent, with the pool area being especially beautiful. It was lovely to sit in the sun beside the pool, drinking a cocktail.
The location is decent, being a short stroll from Ornos Beach. Before arriving in Mykonos, I had planned to walk a lot on the island. It is not advisable to walk on the island roads, as the they are exceptionally narrow and can be dangerous for pedestrians with buses screaming by. This made Ornos itself a bit inconvenient, as to get anywhere I needed to take a bus (which was OK, just not what I had planned).
The service at Yiannaki was excellent. The young woman at the front desk was incredibly helpful from the moment we arrived, offering advice on anything we were interested in.
One thing that disappointed me was the breakfast. I could tell that the hotel did not take pride in their breakfast service, they just seemed to offer it because it was an expectation of guests. They did not make enough food in a timely enough manner to serve guests properly. I arrived right when the doors opened one morning and there were six fried eggs for the 20 people in the room. A bit disappointing. Likely the kitchen was understaffed the time I was there (October).
All that being said, I would still go back and recommend to others, it was a nice hotel, especially for the price I paid in October. Next time, I would rent a car while there and be able to explore the island more fully.