My wife and I had an incredible 1-week stay at the Anastasis apartments. We had read many great reviews of the hotel and the hotel more than met our very lofty expectations!
We stayed in the honeymoon suite which is very spacious and has its own outdoor balcony overlooking the caldera complete with lounge chairs, a dining table with chairs, and an umbrella for shade. There is an indoor hot tub and an outdoor hot tub as well as a shower. They provide you with slippers and robes for comfort and clean everything daily. The kitchen has a microwave, silverware, cups, plates, bowls, etc and also has a fridge which is well stocked (everything in the fridge is free) and they replenish your bottled water supply daily. The bed is very comfortable. On the hotel grounds, there is a lounge area with a computer, many books for reading, a large flat screen TV, and a fireplace. There is also a nice pool overlooking the caldera which is kept extremely clean. In short, the place was beautiful. The location is great as well - it's a 1.5-2 hr walk to Oia and a 30-45 minute walk to Fira. There's also a bus stop nearby (the hotel will provide you with a bus schedule).
During our stay, the "Anastasis Team" was always around to help us with anything we needed - they helped us decide where to eat and what to do, gave us directions to anywhere we wanted to go, booked a sunset cruise for us, arranged for a rental car, etc etc - basically making sure we didn't have to deal with any hassles whatsoever on our trip. The facilities were kept absolutely spotless; they are constantly cleaning. They brought us surprise treats (wines, cocktails, champagne, desserts). And remarkably, even though they seemed to be everywhere at once making sure our stay was memorable, they managed not to disturb us at all. It was the perfect blend of service and privacy.
If you're looking for somewhere to stay on Santorini, you cannot go wrong with Anastasis Apartments - they really take great care of their guests!