Although this restaurant looks pleasant and many have praised it for being traditional with authentic excellent food I'm affraid I would have to disagree. My family comes from Cephalonia and I have been going back every year of my life and although I don't hate the place there are definately much better restaurants in Agia Efimia.
If you are only staying in Agia Efimia for a few days please, please do not waste your money here if its good food you want.
Ever since Penelope Cruz starting visiting this restaurant it has been receiving fantastic reviews from tour books and travellers. However, before the film crew arrived this restaurant was thought of as extremely poor by the locals and tourists and was nearly empty every night.
Agia Efimia does not have that many outstanding restaurants but of the lot I'd recomend Spiros. It many not look pretty but it's authentic and cheap.
One word of advice when eating in a Greek restaurant: Eat Greek food. This many sound obvious but I mention this so that you don't order dishes which Greeks generaly can't cook (like pizza's, as anyone who has eaten a Greek pizza will know).