We stayed 5 days on Kea and had a wonderful and super relaxing time. If you are looking for a small, quiet island, wich is easily accessible from Athens, Kea is a great choice.
The island: 1h by ferry from Lavrio, Kea is super easy to get to. The ferry costs around 50-60 Euros for two people and a car. You'll definitely be needing a car to get around. We didn't have a 4x4 and everything worked out but if you have access to one, it would be a bit easier to get around. The night sky is incredible since there aren't a lot of lights on the Island. We went at the beginning of July and have experiences a very dry and hot time, in which not a lot of green can be found. This is quite typical for Greece at that time but if you are a nature lover who likes to go for walks, I would recommend going earlier in the year since it is super hot during the day and there are not too many high trees to protect you from the sun. We did a couple of walks, all of which were nice but not outstanding. If you want to strech your feet, I would recommend walking down to the archeological site which takes 40 min by car + 45 min walking downhill. If you want to start straight from the house, go to Otzias, George & Isabell will tell you the route.
The house: We agree will all of the comments down below. The view is breathtaking and it is super super quiet. Perfect to relax and recharge. The room really is super clean but also very small and already quite full with two people and two small suitcases. Everything is according to the pictures so we didn't have any surprises. The bathroom is very modern and spacious and is devided from the sleeping area via a sliding door. The space for cooking is definitely not meant to have big dinners. If you are looking for a small space to prepare some breakfast or eat some baguette, everything should work. We tried to actually cook but failed with only a small pot and pan available.
the beds are comfy with rather soft matrasses. Just note that there are two separate beds which are not connected to each other so they drift apart during the night. You'll have your own little areas to eat and chill which gives you some private space if you like to. The view from the pictures can only be experienced from the area in front of the main house though.
Food: Kea has many good restaurants of which George will be able to give you multiple good recommendations, depending on your taste, mood and budget. Everything is a bit more expensive on an Island compared to the mainland and Kea is no exception, just keep that in mind.