Naoussa Tavern offers a great view of the caldera, sunset, and the town of Fira. My wife and I both enjoyed our meals there. She had the moussaka which was outstanding. I had the red snapper, which was also excellent. However, be forewarned that they serve the fish whole; you have to pick out the bones. It was very tasty though!
The staff was also very friendly and understanding when I informed them that I mistakenly left my wallet at our hotel and was unable to pay the bill. They did not make the slightest fuss about it and simply asked us to pay the bill when we returned the following day.