I would highly recommend staying at Lilium. The facility was spacious, clean, and within walking distance to Fira.
Although this facility is not directly on the ocean, it does has an afar view of the ocean and is in close proximity to the caldera, dining, and shopping.
Our host, George, was very accommodating. He went out of his way to arrange transportation and excursions, as well as provide valuable information for dining and sightseeing.
I would definitely stay here again.