With an airport and two ports (Argostoli and Sami), the island receives quite a bit of package tourism but has the space to absorb it and quite a few beaches too. Conveyance is recommended.
Kefallonia is one of the few islands with its own National Park which is primarily a forested mountain and great for hikes and nature walks. There are peninsulas, caves and the fertile Livatho plain upon which to escape the high season hordes as well as several un-developed beaches and coves.
The novel, Captain Corelli's Mandolin by Louis de Berniere's, has Kefallonia as its subject and was recently made into a motion picture.
The islands Greek population peaks in summer when it may reach up to 40,000. as many Kefallonia winter in Athens and return only for holidays or to work the warm season crowds. Fiskardo, in the extreme north, is an over priced yacht Marina with a small bit of charm. Mainland Greeks, amongst themselves, give the 'Kefallonities' a reputation as stubborn, ornery, and even crazy but they aren't fools and island prices are not low. See Eco-Kefallonia and Greek Island Guide Kefallonia