Kassos is not an island for everybody. Its arid with very little shade, there are next to no buses so long walks are de-riguere and its under populated due to immigration and a massacre by the Turks in 1824 from which the island has yet to recover.
Kassos is even difficult to reach being the southernmost Greek island and 6 nautical miles south east of Karpathos between Crete and Rhodes. Although on the ferry routes, when the wind is up, this island is frowned upon by ferry captains.
When you finally do get here you'll find several pebble beaches but no sandy ones and have to caique to neighboring islets for those. The plus side are some lovely little fishing port villages, fresh seafood and friendly islanders. You will find the usual olive groves, sheep and goats. There are a few caves, several churches and 2 monasteries. Very few tourists make it to Kassos but the ones who do are individualists shunning the crowds but not unfriendly. Read about eco-Kassos