I've stayed for four days in Alto Mare and it couldn't been better. The house is just lovely, big rooms, big balcony, big terrace and big kitchen. It was six of us and we didn't have any problem.
Our hosts were very kind and always ready to help us with any problem.
The location is also great as less than five minutes walking to the black beach (beautiful) and fifteen minutes driving from Fira (the capital), which is amazing!
The transport company that take us to every single place was just around the corner so we didn't walk or wait a long time to move around the island.
When I'll go back to Santorini I will definitely go back to Alto Villa without even looking at any other place! FIVE STARS!!!