We stayed at Marble Sun Villa the first week of March. The villa is very well-equipped and the beds are super-comfortable. The views from the terrace are amazing and the villa is within walking distance of everything in Oia. Be prepared -- the villa is down the hill, which means that you have to walk up and down stairs (also, one of the bedrooms is upstairs in the villa). Luckily, Tina arranged for a porter to carry our luggage for us! Tina also arranged for our airport transfers and met us when we arrived. She explained everything to us and attempted to set up tours for us. Since we visited off-season, many of the tours weren't available. However, we visited the volcano (caldera) by boat, saw the red and black beaches, toured the archaeological excavation and also arranged to have massages. We were able to travel around the island by local bus, which was convenient and inexpensive.
Oia was spectacularly beautiful and not crowded. Unfortunately, most restaurants and many shops were closed while we were there. There was a lot of renovation going on in the village, to prepare for high season. A few restaurants, the supermarket and some shops were open. In Fira, much more was open and it was just a short bus ride away. But, it would have been nice to know when I booked that not much would be open in Oia.
It was a great stay, though. I recommend the Marble Sun Villa -- but, plan your travels a little bit later in the year to be able to enjoy the restaurants and bars of Oia.