Can't say enough good things or recommend it highly enough! Beautiful and secluded, and I'm already aching to be back.
Some useful things to keep in mind:
1) Bring LOTS of water. The water is not recommended to drink (though fine for cooking, washing etc), and there was a case already there, but we ended up drinking more than was in the case. I'm also not sure if the water was from the Antonis or the previous guest, so maybe confirm?
2) In terms of getting to Kea from Athens and back to the airport, it took us 40€(taxi from Athens to Lavrio, and another driver quoted us 70€, so be careful)+14€(ferry tickets there, per person)+30€(Lavrio to Kato Meria taxi)+30€(for the housekeeper to take us there and back)+30€(Kato Meria back to port)+12€(ferry tickets back, per person)+50€(taxi from Lavrio to airport), for a total of 206€, more if you have more people. Make sure you have enough cash on the island.
3) Because of all the transfers and such, make sure to leave PLENTY of extra time between pickup time at the house and ferry departure time, like 1 hour+.
4) The coffee maker in the kitchen was a moka pot.
5) The second closest beach was our favourite! And definitely try and get out to the ruins.