I stayed there last year and it was a great hotel. There was no view of the caldera and the only view of the ocean was from the roof of the room. It is also in a small village with not much around. You would definitely need a car if you stayed there.
On the other hand, the rooms (all suites from what I could tell) were outstanding as was the service. They had a great breakfast in the morning, a nice pool and jacuzzi, each with bars next to them. They also have a fitness room with treadmills, lifecycles and weights, which I can't imagine you'd find at other places in Santorini. There's no view and if you're looking for nightlife or beaches, you won't like Vedema unless you have a car. The bottom line is that is a great hotel in a very strange location.