We stayed in one of the rooms with a sea view, and the sea view across the bay to Portoferraio with its buildings, lighthouse and the to and fro of passenger ferries is really worth it. Food in the pleasant restaurant is simple and very good. Breakfast is more than adequate.
If you want a beach, then the one at the hotel is just about sufficient, but if you want to be near the sea in what has an almost village atmosphere next to the little boat harbour, then this is the place for you.
The staff are all very friendly and efficient.
Disadvantages? Without a car real shops are a distance away. (The shop at the hotel is not a subsititute). There are buses, but not many, and the boat shuttle to Portoferraio is a wonderful experience, but not terribly reliable: if the wind is too strong or there don't seem to be enough passengers, then it doesn't run.
But all in all, the ten days we spent at Hotel Mare were excellent and will be repeated.More