My wife and I stayed at Oia Castle for 3 nights in May 2007. Santorini was the first stop for our honeymoon, so we were hoping for nice views and a relaxing atmosphere.
I had arranged for a transfer from the airport (surprisingly small, since I'm used to Hartsfield in Atlanta) and it was a breeze. The first ride up the twisty road to Oia was a little nerve-wracking but gave us a chance to peek at Fira and see the views on the east side of the island. We were met at the bus by an employee of the hotel who was nice enough to carry my wife's bag and refused a tip when we got to our room.
The room itself was very nice, with a little kitchen, and cozy bathroom (don't expect a hot bath on Santorini though, we ran out of hot water before the tub was 1/2 full. I'm sure it's because of tight water control there). We stayed in the Volcano suite which had its own little porch with a table and chairs which we used every evening to watch the sun set. The views were spectacular. The only complaint we have is, there's a little restaurant just up the hill and apparently the family that owns it lives below. Well, every night as everyone is gathering to watch the sun set, a little boy comes out on there porch and starts banging on the grill, yelling at tourists, and generally acting obnoxious. If not for him, the sunsets would have been perfect.
The only other complaint we had was the bugs. For some reason our room wasn't getting the ventilation we expected and the first night there, we hardly slept at all. Some tiny little gnats kept flying around our heads, keeping us awake (not the best way to start a honeymoon).
Overall, I'd recommend this hotel to anyone else. The staff was very friendly and available whenever we needed them. The location is excellent if you want to stay in the quieter part of the island, and you can't beat the view. Sunsets, blue sea, and a fishing village below.

We stayed in the Aqua-Marine suite during summer of 2007. These rooms were incredible! Great decor and layout. The privacy was wonderful - albeit because we had both suites booked. I imagine that wouldn't be the case otherwise.

Every evening before sunset, the crowds line up in that area of Oia, and YOU are floating around in the jacuzzi! We felt like super stars. The view cannot be beat.
The pool in the room was a blast. The jacuzzi outside was nice, but barely lukewarm in temperature.

The suites that we had were definitely 5 star - unfortunately we felt that the service did not quite live up to that. For example, three days in a row we asked the cleaning staff to please wait until later to service our rooms - but as we were trying to relax and enjoy our coffee, the young man was right there with us, cleaning. We tried to communicate with him in both Greek and English, but he did not understand.
As I was lying in a chair one afternoon on our veranda, another staff member asked me to get up so he could see if the cushion needed to be laundered. Strange.

Andrea in the office, however, was quite helpful, kind, and hospitable.

There is a difference between service and hospitality. At Oia Castle you will get good service, but we did not find the hospitality that you'd expect from an expensive 5 star hotel.

All in all, Oia is breathtaking.

On a matter unrelated to the hotel - watch out for 'cruise ship dumps' - when the cruise ships dump thousands of uncurious tourists who crowd the streets trying to find some fridge magnets and Budweiser before they have to be back on the ship for the 4 o'clock buffet...

I love this place! It is a private paradise with the most beautiful sunset view in Santorini. Our room 'Aqua' had its own heated private pool off the bathroom. Incredible! It doesn't get more romantic than this. Swimming together in a privacy, putting on a robe and wandering onto that patio to enjoy some complimentary champagne while watching the sunset. If I return to Santorini I intend to plan my trip around when I can get into the same room.

Certainly this magnificent hotel-boutique corresponds to beauty of island Santorini. We stayed for three nights in Aqua - Marine suite (see photos). Though maybe not absolutely convenient and big rooms. The internal pool is more for design, than for swimming. In a jacuzzi on a terrace water is cold and strongly smelled chlorine (as well as in pool). But as a whole fine impression. The hotel personnel - students from all world. More precisely one girl (the main manager) from Patagonia (Chile) and one guy (the porter and cleaner) from Poland. It was very pleasant to communicate with them. Though there were some misunderstanding (called by hotel taxi for cruise around island has arrived with hour delay as has mistake a city on Santirini. But it is more fault of taxi office). Highly recommended.