Kosta and Elisa's place is a gem, exactly the type of place one hopes to stay when traveling. I was searching for a place that had local flavor (which seemed to be lacking in most of the hotels) and I certainly found it here. The location of the house (a 19th century restored mansion) is amazing, and the photos of the view do not do it justice. Waking up every morning in the sun filled room with a view of the town, harbor, and sea was really very special.
But the best part of staying here is the hosts. Kostas and Elisa clearly love their island and the property they have so lovingly restored, and it shows in how they treat their guests. From meeting me at the port to helping me get tickets to an event at the Apollon Theater to telling me all about the history of the island, Kostas and Elisa were the perfect hosts.
As others have already noted, to reach the house from the town below you have to climb some steps, so I wouldn't recommend it to people with mobility issues.
Aside from that, I agree with all the other guests who have highly recommended Kosta and Elisa's house - the perfect place to stay in beautiful Ermoupoli. I'll definitely visit again and I wouldn't even consider staying anywhere else!